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The Legends Deck glossary defines every MLB Statcast and baseball stat used in the game — each term links to a full explainer with the current 2026 leaders.
301 terms across 7 categories. Browse the blog for guides and deep dives.
A bloop single is a weakly-hit baseball that drops in for a hit between infielders and outfielders, usually with an exit velocity under 70 mph and a launch angle between 25 and 45 degrees.
A cold zone is a specific region of the strike zone where a batter consistently produces below-average results, such as low batting average, high whiff rate, or weak contact.
A GIDP (grounded into double play) occurs when a batter hits a ground ball with a runner on first and fewer than two outs, and the defense records two outs on the play — one of the most rally-killing events in baseball.
A groundball single is a base hit that stays on the ground and reaches the outfield grass or finds a hole in the infield, typically with an exit velocity between 60 and 100 mph and a launch angle below 10 degrees.
A hit by pitch (HBP) awards the batter first base when a pitch strikes him without his swinging at it, boosting on-base percentage while leaving batting average untouched.
A leadoff hitter is the first batter in a team's lineup, whose primary job is to get on base at a high rate, see pitches, and set the table for the middle of the order.
A sacrifice fly is a fly-ball out, hit with fewer than two outs, that scores a runner from base — credited as an RBI and excluded from the batter's at-bat total.
A slash line is a three-number shorthand displaying a batter's Batting Average, On-Base Percentage, and Slugging Percentage separated by slashes — for example, .300/.380/.520 — giving a compact portrait of contact, discipline, and power.
A spray chart is a bird's-eye diagram of a baseball field on which every batted ball a hitter puts into play is plotted by landing location and outcome, making pull tendencies, opposite-field ability, and gap-hitting profiles immediately visible.
A switch hitter is a batter who can hit from both the left and right sides of the plate, choosing the side that gives the platoon advantage against each pitcher.
A Texas leaguer is a softly hit fly ball that drops between the infielders and outfielders for a base hit — too deep for the infield to catch, too shallow for the outfield to reach.
A zone hit is a batted ball that lands in the strike zone or passes through the zone and results in a hit, a concept used in Statcast to evaluate plate coverage and contact quality.
An RBI groundout is a ground ball hit by the batter that results in an out but still allows a runner on third base to score, credited as a run batted in under MLB Rule 9.04.
Attack Angle is the vertical angle of the bat's path at the moment of contact, measured by Statcast bat tracking, indicating whether a hitter is swinging up, down, or level through the ball.
Barrel rate is the percentage of a hitter's batted balls classified as barrels — contact of at least 98 mph exit velocity in a launch-angle window that has historically produced a .500+ batting average and 1.500+ slugging — making it the single best Statcast predictor of sustainable power.
Bat path is the precise three-dimensional angle and trajectory the barrel of the bat travels from the start of the swing to the point of contact.
Bat speed is the velocity of the bat's sweet spot at contact, measured in miles per hour by Statcast's Hawkeye system, with an MLB league average near 71 mph and elite hitters exceeding 75 mph.
Batting average is a hitter's total hits divided by official at-bats, expressed as a three-digit decimal that measures how often a batter gets a hit.
Chase rate is the percentage of pitches outside the strike zone that a batter swings at, measuring plate discipline where a lower number indicates a more selective hitter.
Contact rate (Contact%) is the percentage of a hitter's swings that result in contact with the ball, the inverse of whiff rate and a core plate-discipline metric.
Exit velocity is the speed of the baseball as it leaves the bat on a batted ball, measured in miles per hour by Statcast's Hawk-Eye optical tracking in every MLB stadium; it is the cleanest single measure of raw contact quality.
Fly ball rate (FB%) is the percentage of a hitter's or pitcher's batted balls that are classified as fly balls, a core component of every batted-ball profile.
Hard-hit rate is the percentage of a hitter's batted balls struck at 95 mph or harder off the bat, a Statcast quality-of-contact measure that stabilizes quickly and correlates strongly with power and expected slugging.
HR/FB rate is the percentage of a player's fly balls that become home runs, a measure of raw power for hitters and a key regression signal for pitchers.
ISO (Isolated Power) measures a hitter's raw extra-base power by subtracting batting average from slugging percentage, isolating only doubles, triples, and home runs.
Launch angle is the vertical angle at which the ball leaves the bat after contact, measured in degrees by Statcast's optical tracking.
Line drive rate (LD%) is the percentage of a hitter's batted balls that are classified as line drives, the contact type that produces the highest batting average on balls in play.
On-Base Percentage (OBP) is the rate at which a hitter reaches base via hit, walk, or hit-by-pitch, calculated as (H + BB + HBP) ÷ (AB + BB + HBP + SF).
OPS (On-base Plus Slugging) is the sum of a hitter's on-base percentage and slugging percentage, used as a quick single-number measure of total offensive production.
OPS+ is on-base plus slugging percentage adjusted for park and league context, scaled so that 100 equals league average — a 150 OPS+ means a hitter was 50% better than league average at producing offense.
Pull rate is the percentage of a hitter's batted balls hit to the side of the field they swing toward — left field for right-handed batters, right field for left-handed batters.
RBI (runs batted in) credits a batter for each runner who scores as a direct result of his plate appearance, excluding runs that score on errors or grounded-into double plays.
RISP stands for Runners In Scoring Position — any baserunner on second or third base — and batting average with RISP measures how often a hitter delivers when a single can drive in a run.
Slugging percentage (SLG) is a hitter's total bases divided by at-bats, weighting singles as 1, doubles as 2, triples as 3, and home runs as 4 to measure per-at-bat power output.
Squared-up rate is the percentage of swings on which a hitter transfers at least 80% of the maximum possible exit velocity to the ball, given their bat speed and the incoming pitch speed.
Sweet Spot Percentage is the share of a hitter's batted balls struck with a launch angle between 8 and 32 degrees — the optimal range for producing hits and extra-base damage.
Swing length is the total distance, measured in feet, that the head of the bat travels from the start of a hitter's swing through contact, tracked by Statcast's bat-tracking system.
The Mendoza Line is the .200 batting-average threshold that separates barely-employable major-league hitters from those almost certain to lose their job.
Total bases is the sum of all bases a hitter earns on hits, counting a single as 1, a double as 2, a triple as 3, and a home run as 4.
The three true outcomes are strikeouts, walks, and home runs — plate appearances whose outcomes are decided entirely by the pitcher and hitter with no involvement from fielders.
xBA (expected batting average) is a Statcast metric that estimates what a hitter's batting average should be based on the exit velocity, launch angle, and sprint speed of each batted ball, stripping out luck and defense.
Expected Slugging Percentage (xSLG) is a Statcast metric that estimates a hitter's slugging percentage from exit velocity, launch angle, and sprint speed, stripping out the effects of defense, ballpark, and luck.
A blown save is charged to a relief pitcher who enters in a save situation and allows the tying run to score, forfeiting the lead his team handed him.
A changeup is an off-speed pitch thrown with fastball arm action but at reduced velocity, designed to disrupt a hitter's timing through deception rather than break.
A closer is the relief pitcher a team designates to pitch the final inning of close games to protect a lead and earn the save.
A Collard Green is a heavy, low-spin breaking ball that lacks sharp vertical drop and resembles a flat, deadened curveball.
A curveball is a slow breaking pitch thrown with heavy topspin that drops sharply as it crosses the plate, typically 70-82 mph in MLB.
A cutter is a fastball variant — typically 2-5 mph slower than a four-seamer — that breaks late toward the pitcher's glove side, splitting the difference between a fastball and a slider.
A dead zone fastball is a four-seam fastball whose total movement — the sum of vertical and horizontal break — falls near the league-average magnitude, making it easier for hitters to square up than fastballs at either movement extreme.
A first-pitch strike is any strike — called, swung at, or fouled — on the opening pitch of a plate appearance, and first-pitch strike rate is one of the strongest simple predictors of pitching success.
A fly ball pitcher is a pitcher who induces a high rate of fly balls on batted balls, typically above 40%, trading home runs for strikeouts and weak pop-ups.
A four-seam fastball is baseball's most common pitch — gripped across the horseshoe seams to generate maximum backspin and near-zero horizontal movement, producing the highest velocity and the most carry through the strike zone of any pitch type.
A groundball pitcher is one who induces a high rate of ground balls on batted balls, typically above 50%, using sinkers, splitters, and low pitch location to keep the ball on the dirt.
A hold is a statistic credited to a relief pitcher who enters a game in a save situation, records at least one out, and leaves without surrendering the lead.
A hold is a relief-pitching stat awarded when a pitcher enters in a save situation, records at least one out, and leaves the game with the lead still intact for a teammate to finish.
A hold as a stat is a relief pitcher metric that credits a reliever for preserving a lead in a save situation without finishing the game, bridging the gap to the closer.
A kick change is a modern changeup variant thrown with a spiked or kicked index finger that creates seam-shifted movement, giving pitchers harder, sharper changeups with late drop.
A knuckle-curve is a curveball thrown with one or two fingers spiked (knuckled) against the ball, producing tight, late vertical break with curveball-level spin rates.
A knuckleball is a pitch thrown with minimal spin — typically under 1,500 RPM — that flutters unpredictably toward the plate due to asymmetric airflow across its seams, making it difficult for hitters and catchers alike to track.
A LOOGY — Lefty One-Out GuY — is a relief pitcher used almost exclusively to face left-handed batters in high-leverage spots, a role largely eliminated by MLB's three-batter minimum rule in 2020.
A meatball is a fat, hittable pitch — usually a fastball that catches the middle of the plate or a breaking ball that hangs — served up for the hitter to crush.
A middle reliever is a bullpen pitcher who typically works the fifth through seventh innings, bridging the gap between the starter and the higher-leverage setup man or closer.
A pickoff is a throw from the pitcher or catcher to a fielder covering a base to tag out a baserunner who has strayed too far from the bag.
A pitch mix (or arsenal) is the complete set of pitch types a pitcher throws and how often he throws each one — the combination of velocity, movement, and usage rates that defines his approach.
A pitcher win is a statistic awarded to the pitcher credited with the victory when their team takes the lead and never relinquishes it.
A pitchout is a deliberate ball thrown outside the strike zone on an expected stolen-base attempt, designed to give the catcher a clear throwing lane to nail the runner.
A quality start is any starting-pitcher outing of at least six innings with three or fewer earned runs allowed — a binary credit for keeping the team in the game.
A reliever win is awarded to a relief pitcher who enters a game when their team is tied or trailing, takes the lead while in the game, and their team never relinquishes that lead through the remainder of the game.
A save is a statistic credited to a relief pitcher who finishes a game won by their team while meeting MLB Rule 9.19 criteria — generally entering in a tight spot and protecting a lead of three runs or fewer.
A save opportunity is any situation in which a relief pitcher enters a game eligible to earn a save — and it is the denominator behind save percentage, the standard measure of closer reliability.
A setup man is a relief pitcher, usually a team's second-best bullpen arm, who pitches the eighth inning (or another high-leverage spot before the ninth) to hand a lead to the closer.
A shutout is a complete game pitched by one starter who allows zero runs across the entire game, credited only when the pitcher records every out without relief and the opposition does not score.
A sinker is a fastball variant with arm-side run and downward movement that induces ground balls, thrown 88-96 mph with a spin axis tilted toward the throwing arm.
A six-man rotation is a pitching staff structure in which six starting pitchers take turns starting games, giving each starter five days of rest between outings instead of the traditional four.
A slider is a breaking pitch thrown between 78 and 92 mph that moves laterally and downward, sitting between a fastball and a curveball in velocity and break.
A slurve is a breaking pitch that combines the horizontal sweep of a slider with the downward bite of a curveball, traveling 78–84 mph with a diagonal 11-to-5 shape.
A splitter is an off-speed pitch thrown with the index and middle fingers split wide on the ball, producing sharp late downward movement at near-fastball velocity.
A sweeper is a breaking pitch thrown in the low-to-mid 80s with exaggerated horizontal break—often 15 to 20 inches—and minimal vertical drop, classified by Statcast as a distinct pitch from the traditional slider.
A swingman is a pitcher who moves between the starting rotation and the bullpen as needed, making spot starts, covering long relief, and filling gaps caused by injuries, off-days, or doubleheaders.
A two-seam fastball is a fastball gripped along the narrow parallel seams of the baseball, producing arm-side run and natural downward movement that generates weak contact and groundballs.
An immaculate inning is a half-inning in which one pitcher strikes out all three batters on exactly nine pitches — every pitch a strike, no contact, no balls.
An inherited runner is a baserunner who reaches base against one pitcher but is charged to that pitcher even after a reliever enters and either strands or allows the runner to score.
An opener is a relief pitcher used to start a game and work only the first inning before handing off to a bulk reliever, designed to neutralize the top of the order and dodge the times-through-the-order penalty.
Arm angle is the angle in degrees between a pitcher's shoulders and the line from shoulder to ball release, where 0° is sidearm, 90° is straight overhead, and negative values are submarine.
Arm speed measures the peak rotational velocity of a pitcher's throwing arm, recorded in revolutions per minute (RPM) by Statcast biomechanics tracking.
BABIP for pitchers measures the rate at which balls put in play against a pitcher fall for hits, serving as a key indicator of luck and defense.
Batting average against (BAA) is the batting average that opposing hitters compile off a pitcher, calculated as hits allowed divided by at-bats faced.
Bauer Units (BU) measure fastball spin rate divided by velocity, expressing how much spin a pitcher generates per mile per hour.
BB/9 (walks per nine innings) measures how many batters a pitcher walks per nine innings pitched, the standard rate stat for command and control.
CRA (Core Run Average) is a predictive pitching metric that estimates a pitcher's true run allowance per nine innings by combining strikeouts, walks, hit-by-pitches, and home runs allowed.
CSW (Called Strikes plus Whiffs) Rate is the percentage of a pitcher's total pitches that result in either a called strike or a swinging strike, capturing both command and stuff in one number.
Deserved Run Average (DRA) is a pitcher evaluation metric created by Baseball Prospectus that estimates the runs a pitcher deserves to allow per nine innings using a mixed model that accounts for count, base, and quality of contact.
DRA (Deserved Run Average) is Baseball Prospectus's run-prevention metric that estimates how many runs a pitcher deserved to allow per nine innings after stripping out the influence of defense, framing, park, and opponent quality.
ERA (Earned Run Average) is the number of earned runs a pitcher allows per nine innings, calculated as (Earned Runs × 9) ÷ Innings Pitched.
FIP (Fielding Independent Pitching) is a pitcher's ERA estimator built only from strikeouts, walks, hit-by-pitches, and home runs — outcomes the pitcher controls directly, independent of the defense behind him.
Four-seam fastball velocity is the speed of a pitcher's primary fastball as measured by Statcast at the point of release, typically 55 feet from home plate, and is the most important raw physical attribute for a pitcher.
Game Score is a single-number metric created by Bill James that grades an individual starting pitcher's performance in one game, where 50 is average and 100+ is historically elite.
Ground Ball Rate (GB%) is the percentage of balls put in play — excluding home runs — that travel along the ground, and it is the primary batted-ball metric for gauging a pitcher's ability to suppress extra-base contact and generate double plays.
Gyro spin is the rotational component of a baseball that spins like a spiral football pass, contributing no movement to the pitch's trajectory but heavily influencing its aerodynamic drag and perceived velocity.
Gyroscopic Break measures the perpendicular movement of a pitch deviating from its gyro spin axis, quantifying how much late sweep or dive a baseball experiences.
Horizontal Approach Angle (HAA) is the side-to-side angle in degrees at which a pitch crosses the front of home plate, measuring how sharply a pitch cuts across the strike zone from the hitter's view.
Horizontal break measures how many inches a pitch moves side-to-side relative to a spinless trajectory, capturing the arm-side run or glove-side sweep a hitter has to track from release to the plate.
HR/9 (home runs allowed per nine innings) is a rate stat that measures how often a pitcher gives up home runs, normalized to a full game's workload — calculated as (HR ÷ IP) × 9.
Induced Vertical Break (IVB) is the amount of vertical movement on a pitch caused by spin and aerodynamics after the effect of gravity is subtracted, measured in inches by Statcast.
K-BB% (strikeout rate minus walk rate) measures a pitcher's ability to generate strikeouts while limiting walks, making it one of the most stable and predictive single-number indicators of pitching quality.
K/9 is a rate stat that expresses how many batters a pitcher strikes out per nine innings of work, providing a workload-normalized view of swing-and-miss production.
Leverage Index (LI) quantifies the importance of any plate appearance by measuring how much the game's win probability could swing on its outcome relative to an average situation, where 1.0 is league-average leverage.
LOB% (left-on-base percentage, also called strand rate) measures the share of baserunners a pitcher prevents from scoring; league average sits around 72-73%.
Location+ is a Stuff+ family pitching metric that grades how well a pitcher locates each pitch given the count, batter handedness, and pitch type, scaled so 100 is league average and 10 points equals one standard deviation.
Perceived velocity is the effective speed of a pitch as experienced by the hitter, adjusting raw release velocity for the pitcher's extension toward home plate.
Pitch calling is the strategic process of selecting which pitch type and location to throw in a specific count to maximize the odds of recording an out against a specific hitter.
Pitch sequencing is the deliberate order in which a pitcher throws pitch types and locations across an at-bat to exploit a hitter's timing, eye level, and swing decisions.
Pitch tunneling is the technique of throwing different pitches along the same visible path for as long as possible, so the hitter can't distinguish them before the swing decision point roughly 23–25 feet from home plate.
Pitch value measures how many runs above or below average a pitcher generates from a specific pitch type by summing the change in run expectancy for every pitch of that type thrown.
Pitcher extension is the distance in feet from the front of the pitching rubber to where the pitcher releases the ball, measured by Statcast — longer extension makes a fastball play faster than its radar-gun reading.
Pitching+ is a FanGraphs model that combines Stuff+ (pitch shape quality) and Location+ (command quality) into a single 100-scaled metric, where 100 is league average and every point above represents roughly 1% better expected run prevention.
Release point is the three-dimensional coordinate where a pitcher's hand lets go of the baseball, captured in feet by Statcast and used to evaluate arm slot, command consistency, and pitch deception.
Relief Probability of Added Stress (RPAS) is a Statcast metric that quantifies the likelihood a relief pitcher enters a game and immediately faces a high-leverage, stressful situation.
Seam-shifted wake is non-Magnus pitch movement created when the orientation of a baseball's raised seams steers airflow, producing break that pure spin physics can't explain.
Spin axis is the orientation of a baseball's rotational axis as it travels toward home plate, expressed as a clock-face direction that determines whether a pitch carries, sinks, cuts, or sweeps.
Spin efficiency is the percentage of a pitch's total spin that actually creates movement — the rest is gyrospin that contributes nothing to break.
Spin rate is the number of times a pitched baseball rotates around its axis per minute (RPM), measured by Statcast, and is a primary driver of pitch movement and swing-and-miss rates.
Stuff+ is a pitch-quality model that rates the physical nastiness of a pitch — velocity, spin, and movement — on a scale where 100 is MLB average and every 10 points equals one standard deviation.
Swinging strike rate (SwStr%) is the percentage of a pitcher's total pitches that result in a swing-and-miss, measuring raw bat-missing ability across every pitch thrown.
The bullpen is a team's group of relief pitchers, and the physical area where they warm up, responsible for finishing games the starter does not complete.
The eephus is an ultra-slow, high-arcing lob pitch — typically 45 to 65 mph — designed to disrupt a hitter's timing by appearing 30-plus mph slower than a pitcher's fastball.
The ghost fork is a high-spin, split-fingered fastball variation that acts like a splitter but features the pronounced downward, late-biting drop of a traditional forkball.
A screwball is a rare breaking pitch that moves opposite of a curveball — fading and dropping toward the pitcher's arm side — created by pronating the wrist outward at release rather than supinating it.
Vertical Approach Angle (VAA) is the downward angle at which a pitch crosses home plate, measured in degrees, and is the key Statcast metric for explaining why some fastballs miss bats at the top of the zone.
Whiff rate is the percentage of a batter's swings that miss the ball, calculated as swings-and-misses divided by total swings; it is the cleanest single measure of a pitch's bat-missing ability.
WHIP (Walks plus Hits per Inning Pitched) measures how many baserunners a pitcher allows per inning, calculated as walks plus hits divided by innings pitched.
xERA is Statcast's expected ERA estimator, built from a pitcher's quality-of-contact data, strikeouts, and walks to predict run prevention skill independent of defense and sequencing luck.
xFIP (Expected Fielding Independent Pitching) is a defense-neutral ERA estimator that normalizes a pitcher's home run rate to league average, isolating only the outcomes pitchers control: strikeouts, walks, and fly balls.
Zone Rate (Zone%) is the percentage of total pitches a pitcher throws inside the rulebook strike zone, and is the primary single-number indicator of command and willingness to challenge hitters.
An assist in baseball is credited to any fielder who throws, deflects, or otherwise touches the ball in a way that contributes to recording an out — shown as A in a box score and paired with putouts (PO) to describe a fielder's defensive activity.
Arm strength is the Statcast metric measuring a fielder's maximum throwing velocity in miles per hour, used to grade outfield arms and infielder throwing tools.
Catch Probability is a Statcast metric that estimates the likelihood — expressed as a percentage from 0 to 100 — that a major-league outfielder will catch a specific fly ball or line drive, based solely on the distance to the landing zone and the time available to get there.
Catcher framing is the skill of converting borderline pitches into called strikes through pitch receiving, measured by Statcast as the difference between actual and expected called-strike rate in the shadow zone.
Defensive Runs Saved (DRS) is a comprehensive fielding metric that estimates how many runs a defender saves or costs his team relative to an average player at his position.
OAA (Outs Above Average) is Statcast's primary defensive metric, measuring how many outs a fielder converts above or below what an average fielder would produce given identical opportunities.
Pop time is the number of seconds from the instant a pitch hits the catcher's mitt to the instant the ball reaches the fielder's glove at the base on a throw to second or third, measuring a catcher's total throw-down quickness.
Sprint speed is a player's average peak running speed in feet per second, measured by Statcast across their fastest one-second window on qualified runs; it is the cleanest single measure of raw athletic speed in baseball.
The shift is a defensive alignment that positions three or more infielders on one side of second base to take away pull-heavy hitters' most likely ground-ball zones — a strategy banned in MLB starting with the 2023 season.
UZR (Ultimate Zone Rating) measures a fielder's total defensive value in runs above or below an average player at the same position, combining range, errors, double plays, and outfield arm strength.
A barrel is a batted ball with the optimal combination of exit velocity and launch angle that historically results in a minimum .500 batting average and 1.500 slugging percentage.
A gem is a standout, exceptionally high-quality pitching performance in a baseball game, characterized by dominant stat lines and near-flawless execution.
Pop-Up Rate (PO%) is the percentage of a batter's batted balls that are hit weakly into the infield with a launch angle between 10 and 40 degrees, resulting in an easy out.
A Quality At-Bat (QAB) is a statistical metric that grades a hitter's plate appearance based on productive outcomes, specifically rewarding seeing a high number of pitches, drawing walks, executing productive outs, and hitting the ball hard.
An ace is the undisputed top starting pitcher on a Major League Baseball staff, responsible for anchoring the rotation and facing the opponent's best lineup.
BABIP (Batting Average on Balls in Play) measures how often a hitter reaches base on balls put in play, excluding home runs and strikeouts, with league average hovering near .300.
BsR (Base Running Runs) is FanGraphs' all-in-one baserunning metric that measures how many runs a player adds or costs his team on the bases — including stolen bases, extra-base advancement on hits, and double-play avoidance — relative to a league-average runner.
Catcher Framing Runs (CAB) is an advanced metric that quantifies the number of runs a catcher saves or costs their team by getting called strikes on pitches outside the strike zone.
Clutch is a FanGraphs metric that measures how much better or worse a player performed in high-leverage situations compared to his own context-neutral production.
ERA+ (Adjusted ERA Plus) is a park- and league-adjusted version of ERA where 100 equals league average and every point above 100 means the pitcher allowed 1% fewer runs than a typical pitcher in the same conditions.
fWAR and bWAR are the two public versions of Wins Above Replacement — FanGraphs' fWAR builds pitcher value from FIP, while Baseball-Reference's bWAR builds it from actual runs allowed, so the same pitcher can have very different WAR totals.
Hard contact in baseball measures the percentage of balls in play that a batter hits with an exit velocity of 95 mph or greater.
K% (strikeout rate) is the share of plate appearances ending in a strikeout, calculated as strikeouts divided by plate appearances, and used to measure both hitter contact ability and pitcher dominance.
Pace is a Statcast metric that measures the average time a pitcher takes between releasing one pitch and releasing the next.
Pitch framing is the catcher's technique of receiving borderline pitches without shifting their glove, increasing the probability of a called strike.
Plate discipline is a hitter's ability to swing at pitches in the strike zone, take pitches outside of it, and avoid expanding the zone with two strikes.
Pythagorean Winning Percentage estimates a team's expected winning percentage from runs scored and runs allowed using the formula RS² / (RS² + RA²), revealing teams that are over- or under-performing their underlying run differential.
QAB% (Quality At-Bat Percentage) measures the rate at which a hitter produces a positive outcome in a plate appearance based on specific offensive criteria.
RC+ (Weighted Runs Created Plus) is a park-adjusted metric that measures a hitter's total offensive production by runs created, scaled to 100.
RE24 (Run Expectancy based on the 24 base-out states) measures how many runs a player added or cost his team by tracking the change in expected runs before and after each plate appearance.
Replacement level is the baseline production expected from a freely available player — a AAA call-up, waiver claim, or emergency fill-in — against which WAR measures every player's contribution in wins above that floor.
Run Expectancy (RE) is a sabermetric metric that calculates the average number of runs scored from a specific base-out state to the end of an inning.
Run prevention is the comprehensive art and science of limiting opposing teams from scoring, encompassing pitching, fielding, and defensive positioning.
Run Value is a Statcast metric that measures how many runs a single pitch, plate appearance, or season's worth of events added or subtracted relative to league average, calculated from the run expectancy matrix.
SIERA (Skill-Interactive ERA) is an ERA estimator that predicts a pitcher's true run-prevention skill from strikeouts, walks, and batted-ball mix while accounting for how those skills interact.
The Crawford Boxes are a famous seating section in left field at Minute Maid Park that sits just 315 feet from home plate, significantly altering home run and defensive outcomes.
The Pitching Savant Page is the dedicated Baseball Savant dashboard that breaks down a pitcher's entire Statcast arsenal, pitch by pitch.
VORP (Value Over Replacement Player) measures how many more runs a player contributes than a freely available replacement-level player would at the same position in the same playing time.
Walk rate (BB%) is the percentage of a hitter's or pitcher's plate appearances that end in a base on balls, measuring plate discipline for hitters and command for pitchers.
WAR (Wins Above Replacement) measures how many wins a player contributes above what a freely available replacement-level player would provide, combining offense, defense, baserunning, and pitching into a single number.
Platoon splits measure how a hitter or pitcher performs against same-handed versus opposite-handed opponents — the foundation of lineup and bullpen strategy.
wOBA (weighted On-Base Average) is a rate stat that credits each offensive event — walk, single, double, triple, home run — by its actual run value, then scales the result to the familiar OBP range.
Win Probability Added (WPA) measures how much each plate appearance changes a team's probability of winning, summed across a full season, to quantify a player's clutch contribution to actual wins.
wRC+ (Weighted Runs Created Plus) is a park- and league-adjusted measure of total offensive value where 100 is league average and every point above or below equals one percent better or worse than average.
xwOBA (expected weighted On-Base Average) is Statcast's quality-of-contact metric that estimates what a hitter's wOBA should be based purely on exit velocity, launch angle, and (for speed-dependent balls) sprint speed.
ZiPS is a player projection system created by Dan Szymborski that forecasts MLB hitter and pitcher performance using weighted historical data, similarity scores, and empirical aging curves.
3-up, 3-down in baseball describes a half-inning in which a pitcher faces exactly three batters and retires all of them, allowing no hits, walks, or baserunners — also called a 1-2-3 inning.
A backwards K is the scorekeeping symbol for a strikeout looking — when the batter takes called strike three without swinging.
A balk is an illegal pitching motion with runners on base that the umpire judges to deceive the runner — the ball is dead and every runner advances one base.
A double play is a single defensive sequence that records two outs on one batted ball or play, most commonly a ground ball turned shortstop-to-second-to-first.
A fielder's choice is when a batter reaches base only because the defense chose to put out a different baserunner instead of throwing him out, crediting no hit.
A fielder's option is a scoring decision where a fielder chooses to retire a lead runner instead of the batter, and the batter is not credited with an RBI even if a run scores on the play.
A force out occurs when a runner is put out at a base he is required to advance to because the batter became a runner, and the fielder only needs to touch the base with the ball.
A foul tip is a batted ball that nicks the bat and goes directly and sharply into the catcher's glove or hand, is caught legally, and counts as a strike — it is a live ball, not a dead ball, and runners may advance.
A full count is a 3-2 count — three balls and two strikes — where the next non-foul pitch decides the plate appearance with a walk or a strikeout on the line.
A passed ball is a pitch that the catcher should have caught or controlled with ordinary effort but fails to, allowing a baserunner to advance — charged to the catcher, not the pitcher.
A perfect game is a complete game in which a single pitcher (or pitchers) retires all 27 batters faced, allowing no hits, no walks, no hit-by-pitches, and no baserunners of any kind.
A plate appearance is the official record of a batter completing their turn at bat, regardless of the outcome.
A rundown, or pickle, is a defensive play in which a baserunner is trapped between two bases and fielders throw the ball back and forth to tag him out.
A single in baseball is a base hit on which the batter reaches first base safely and stops there, earned without the aid of an error or a fielder's choice — the shortest and most common of the four types of hit.
A swing-off in baseball is the All-Star Game tiebreaker that replaces extra innings with a Home Run Derby-style mini-contest: each side picks three hitters who take three swings apiece, and the team that hits the most home runs wins.
A triple play is a single defensive sequence in which the fielding team records three outs on one batted ball, the rarest routine play in baseball.
A walk-off is a play in which the home team scores the winning run in the bottom of the ninth inning or later, ending the game instantly because the visiting team has no further at-bat.
A wild pitch is a pitch so high, wide, or low that the catcher cannot control it with ordinary effort, allowing a baserunner to advance, charged to the pitcher rather than the catcher.
The ABS Challenge System is MLB's 2026 rule letting the pitcher, catcher, and batter each challenge a ball-or-strike call using Hawk-Eye tracking data, without replacing home plate umpires entirely.
Hitting for the cycle is when a single batter records a single, double, triple, and home run in the same game — one of baseball's rarest individual feats, rarer than a no-hitter.
The designated hitter (DH) is a player who bats in place of the pitcher every time the pitcher's spot comes up, without ever playing the field.
The ghost runner is an automatic runner placed on second base at the start of each extra-inning half-inning in MLB regular-season games, introduced in 2020 and made permanent in 2023.
The Golden At-Bat is a proposed MLB rule that would allow a team to send its best hitter to the plate in a late-game, high-leverage situation regardless of the batting order.
The infield fly rule automatically retires the batter on a fair pop-up an infielder can catch with ordinary effort when there are runners on first and second (or bases loaded) with fewer than two outs — preventing fielders from intentionally dropping the ball for cheap double plays.
A team's magic number is the combined total of its own remaining wins plus its closest pursuer's losses required to mathematically clinch a playoff spot or division title — when it hits zero, the spot is secured.
The neighborhood play is the long-standing infield practice of getting the force out at second base while being merely close to the bag — a safety-driven gray area that replay review has largely eliminated.
The pitch clock is an MLB rule introduced in 2023 that limits time between pitches—15 seconds with bases empty, 18 with runners on—and cut average game time by 24 minutes in its first season.
The robot umpire, or Automated Ball-Strike System, is a technology that uses cameras and software to call balls and strikes without human home-plate umpires.
The strike zone is the rulebook three-dimensional space over home plate, from the midpoint between the batter's shoulders and waist down to the hollow beneath the kneecap, in which a pitch that is not swung at is called a strike.
A Wild Card is an MLB playoff berth awarded to the top non-division-winning teams in each league by record, giving three extra clubs per league a postseason spot.
A club option is a contract provision that gives a team the unilateral right to extend a player's contract for one or more additional years at a pre-specified salary, in exchange for paying a smaller buyout if the team declines.
A farm system is the network of minor league affiliates an MLB team uses to develop drafted and signed players until they are ready for the majors.
A minor league option lets a team freely send a player on the 40-man roster to the minors during a season; each player gets three option years, with a possible fourth under the 2022 CBA.
A no-trade clause is a contract provision giving an MLB player the right to veto any trade — either to all 29 other teams (full NTC) or to a specified list (limited NTC).
A non-tender is when an MLB team declines to offer a contract to one of its arbitration-eligible players by the annual tender deadline, instantly making the player a free agent.
A player option is a contract clause that gives the player — not the team — the sole right to decide whether to play another year at a set salary or become a free agent.
A probationary period is a 45-day window at the start of a Major League Baseball season during which teams cannot option certain veteran players to the minor leagues without their consent.
A rehab assignment is a temporary minor-league stint that lets an injured major-league player return to game action and rebuild timing before being activated from the injured list.
A two-way player is a major leaguer who both pitches and hits as a regular position player or designated hitter, contributing real value on both sides of the ball in the same season.
A walk year is the final year of a player's existing contract before they become a free agent, named for their ability to walk away and sign with any team on the open market.
An opt-out clause is a contract provision allowing a player to terminate the remaining years of his deal and become a free agent at a specified point.
An outright assignment is the transaction that removes a player from the 40-man roster and sends him to the minors after he has cleared outright waivers, without another club claiming his contract.
Deferred money is salary a player agrees to be paid in future years — often long after the contract ends — lowering the deal's present-day cost and luxury-tax hit.
Designated for Assignment (DFA) is an MLB roster move that removes a player from the 40-man roster, opening a seven-day window for the team to trade, waive, outright, or release him.
MLB salary arbitration is the contract process for players with 3-6 years of service time where, if the player and team can't agree on a salary, an independent panel must choose between the two filed figures with no compromise allowed.
Service time is the count of days a player spends on an MLB active roster or injured list, where 172 days equals one full service year and accrual unlocks arbitration at three years and free agency at six.
Super Two is the designation given to the top 22% of MLB players with between 2 and 3 years of service time, granting them an extra year of arbitration eligibility before free agency.
The 10-and-5 rule gives a player automatic full no-trade protection once he has accrued 10 years of MLB service time, including the last 5 consecutive years with his current team.
The 40-man roster is the group of players under MLB contract who occupy a team's 40 player slots, are protected from the Rule 5 Draft, and form the pool from which the 26-man active roster is drawn.
The injured list (IL) is MLB's roster mechanism for sidelining medically restricted players, freeing the 26-man spot for replacements while preserving the player's service time and full salary.
The luxury tax, formally MLB's Competitive Balance Tax, is a graduated penalty paid by teams whose payroll exceeds annual thresholds set in the Collective Bargaining Agreement, with rates that escalate by tier and by repeat-offender status.
The MLB Draft is the annual amateur draft in which all 30 teams select eligible high school, college, and junior college players, assigning each club exclusive rights to sign the amateurs it picks.
The posting system is the formal process by which a player under contract to a Japanese (NPB) or Korean (KBO) club is made available to MLB teams, who then pay a release fee to the player's original team based on the size of the MLB contract signed.
The Qualifying Offer (QO) is a one-year guaranteed contract offered to pending free agents, designed to compensate their former team with draft picks if they sign elsewhere.
The qualifying offer is a one-year guaranteed contract a team can extend to its own impending free agent at the average of the top 125 MLB salaries — declining it attaches draft-pick compensation that depresses the player's market value.
The Rule 5 Draft is an annual MLB event held during the Winter Meetings that lets teams select unprotected minor-league players from other organizations, with strict roster rules designed to prevent talent hoarding.
Waivers is the MLB transaction process by which a team makes a player available to all other clubs, who can claim him in reverse order of standings before he can be removed from the 40-man roster or sent to the minors.
A ball in play is any batted ball that lands in fair territory and is not a home run, strikeout, walk, or hit-by-pitch — the subset of plate appearances where fielders have a chance to record an out and batters rely on batted-ball luck.
A 'banjo hitter' is a baseball slang term for a weak-hitting player who relies on contact and speed rather than power.
A Blast is a Statcast bat-tracking classification for a swing that both squares the ball up and arrives with fast bat speed — the rarest and most damaging type of contact a hitter can make.
A bullpen game is a game a team plays without a traditional starting pitcher, instead covering all nine innings with a sequence of relievers each throwing one to three innings.
A 'can of corn' is old baseball slang for a high, easy-to-catch fly ball hit to the outfield.
A caught stealing (CS) is charged when a baserunner attempting to steal a base is tagged out before reaching it, ending both the attempt and often the inning's momentum.
A cleanup hitter in baseball is the batter who hits fourth in the lineup, traditionally the team's most dangerous power hitter, whose role is to drive in the runners set up by the first three hitters — 'cleaning up' the bases.
A five-tool player is a position player who grades plus-or-better at all five core baseball skills: hitting for average, hitting for power, running speed, fielding ability, and throwing arm.
A grand slam is a home run hit with the bases loaded, scoring four runs on a single swing.
A ground rule double is a two-base award given to a batter when a fair ball bounces over or becomes lodged in an outfield wall, fence, or other obstacle, with all runners advancing two bases from their position at the time of the pitch.
A hangup is a baserunning sequence where a runner is caught in a rundown between two bases, forcing the defense to execute a series of rapid throws to apply the tag.
A hit-and-run is a coordinated offensive play in which the baserunner takes off with the pitch and the batter is obligated to swing, staying out of a double play and opening holes in the infield.
A hold is a statistic credited to a relief pitcher who enters a game in a save situation, records at least one out, and leaves without surrendering the lead — it is the setup pitcher's version of a save.
A hold in fantasy baseball is a scoring category that credits a reliever for preserving a lead in a save situation without finishing the game, making setup men and middle relievers fantasy-relevant.
The hot corner is the third-base position in baseball, so named because batted balls reach the fielder faster and harder than at any other infield position.
The left fielder is the outfielder positioned in left field, responsible for covering the area between third base and center field and typically possessing the weakest arm of the three outfield positions.
A live ball is the period of play when the umpire has signaled play and the ball is in play, allowing runners to advance, fielders to make outs, and the defense to attempt pickoffs or tag plays.
A mound visit is a stoppage of play where a coach, manager, or catcher walks to the pitcher's mound to discuss strategy, check on the pitcher's health, or delay the game, with MLB teams limited to six visits per nine innings in 2024.
A no-hitter is a complete game in which a pitcher or combination of pitchers allows the opposing team zero hits over at least nine innings.
A phantom ball is a baseball term for a pitch that appears to vanish or change trajectory mid-flight due to a combination of spin axis, release point, and seam-shifted wake, making it one of the most deceptive pitches in modern baseball.
A pinch hit is an at-bat taken by a substitute batter who replaces the scheduled hitter, usually in a high-leverage situation where the manager wants a favorable matchup.
A pinch hitter is a substitute batter sent up to hit in place of a scheduled hitter, who is then removed from the game for the rest of the contest.
A pinch runner is a player substituted into the game specifically to replace a base runner, usually for speed, without affecting the batting order's defensive alignment.
A player to be named later (PTBNL) is a trade component in which the acquiring team receives an unspecified minor leaguer, chosen from an agreed list or by a deadline after the deal.
A putout is the fielding credit awarded to the defensive player who physically records an out — by catching a fly ball, tagging a runner, stepping on a base for a force, or receiving strike three.
The right fielder is the outfielder positioned in right field, responsible for covering the area between first base and center field and typically possessing the strongest throwing arm of any outfielder.
A sacrifice bunt is when a batter deliberately bunts to advance a runner, allowing himself to be thrown out — the batter is not charged with an at-bat in exchange for moving the runner.
The shortstop is the infielder positioned between second and third base, responsible for covering the largest defensive area on the infield and typically the best fielder on the team.
A split-finger fastball is a pitch thrown with the same arm speed as a fastball but with the index and middle fingers spread wide across the seams, causing it to drop sharply near the plate.
A stolen base is credited when a baserunner advances to the next base on his own — without a hit, walk, error, or other event forcing the advance — usually by breaking for the base as the pitcher delivers.
A tag up is the act of a base runner returning to and touching their base after a fly ball is caught before attempting to advance to the next base.
A utility player is a position player who competently plays multiple defensive positions, giving managers lineup flexibility instead of being locked into one spot.
A walk-off win is a home team victory that occurs when the home team scores the go-ahead run in the bottom of the ninth inning or later, ending the game immediately.
An aging curve maps how a baseball player's performance changes as a function of age — rising through development, peaking in the mid-to-late 20s, and declining through the 30s — and serves as the foundation for multi-year statistical projections.
An error is a defensive misplay charged by the official scorer when a fielder fails to convert an out that ordinary effort would have produced, allowing a batter or runner to advance.
An unearned run is a run that scores as the direct result of a fielding error or passed ball rather than the pitcher's own performance, and it counts on the scoreboard but not toward ERA.
Arm action refers to the specific path, timing, and fluidity of a pitcher's throwing arm during the delivery, heavily influencing pitch deception, velocity, and injury risk.
Arm slot is the vertical angle at which a pitcher releases the ball, measured in degrees relative to the ground, heavily influencing pitch movement and platoon splits.
Arm-side run is the horizontal movement of a pitch toward the pitcher's throwing-arm side, generated by lateral spin and gravity.
Caught Stealing Probability (CS Prob) is a Statcast metric that calculates the likelihood of a baserunner being thrown out attempting to steal a base, expressed as a percentage from 0% to 100%.
Difficulty of Lift is a Statcast metric that quantifies how hard a batted ball is to field by combining exit velocity, launch angle, and hang time.
Fastball spin refers to the rate of revolutions a baseball makes on a four-seam or two-seam fastball, dictating its movement, induced vertical break, and perceived velocity.
Fielding percentage measures the rate at which a fielder successfully handles the chances he reaches, calculated as putouts plus assists divided by total chances.
FRV (Fielding Run Value) is Statcast's all-encompassing defensive metric that converts a fielder's range, arm, and positional skills into the number of runs he saved or cost his team relative to average.
Glove-side break is the horizontal movement of a pitch toward the pitcher's glove side, generated by lateral Magnus force, cutting the ball away from the arm side.
Park factor is a ratio that captures how much a specific ballpark inflates or depresses offensive events (runs, home runs, hits) relative to a neutral environment.
Pitch shape is the geometric movement profile of a pitch, defined by its vertical and horizontal break, release point, and approach angle.
PitchCom is the MLB-approved encrypted wearable that lets catchers send pitch type and location calls electronically to pitchers and fielders, replacing traditional finger signs.
Range Factor measures how many defensive plays a fielder makes per game or per nine innings by summing putouts and assists, estimating how much ground a defender covers.
Spin mirroring is pairing two pitches whose spin axes point in nearly opposite directions, so they look identical out of the hand but break in opposite directions.
Sprint Effort is a Statcast metric that measures the percentage of a runner's maximum top speed they achieve when advancing on the basepaths.
Sprint Speed Efficiency is a Statcast-derived metric that measures how effectively a baserunner or fielder converts his maximum physical sprint speed into usable, directional speed toward a base or the baseball.
Sprint Speed to Third measures how quickly a runner accelerates from home plate to third base, providing a granular look at a player's raw baserunning ability.
Statcast is MLB's radar-and-camera tracking system that measures every pitch, swing, and sprint at the major-league level.
The 20-80 scouting scale is the industry-standard grading system pro scouts use to rate baseball tools, where 50 is MLB-average, 80 is elite, and 20 is well below replacement level.
The Cy Young Award is given annually to the best pitcher in each MLB league, as voted on by the Baseball Writers' Association of America.
A forkball is an off-speed pitch thrown with the index and middle fingers spread wide around the ball, producing low spin and a sharp downward tumble that mimics a fastball before falling out of the strike zone.
The Gold Glove is the annual award given by Rawlings to the best defensive player at each position in each league, blending coach-and-manager voting with advanced fielding metrics.
The Silver Slugger Award is given annually to the best offensive player at each position in both the American and National League, as voted on by MLB managers and coaches.
The MLB trade deadline is the single annual date, set within a league-determined window in late July or early August, after which teams can no longer trade players on their 40-man rosters.
The Triple Crown is the feat of leading your league in batting average, home runs, and RBI in a single season (hitters), or in wins, ERA, and strikeouts (pitchers).
Tommy John surgery reconstructs a torn ulnar collateral ligament in the elbow with a tendon graft, with a 12-18 month return-to-pitch timeline and an 80-85% success rate.
xwOBAcon (expected wOBA on contact) measures the quality of a hitter's contact alone — exit velocity and launch angle on balls actually hit — stripping out strikeouts, walks, and luck.
Zone Rating (ZR) is a defensive metric that measures the percentage of balls hit into a fielder's defined zone that he successfully converts into outs.