What is Stuff+? Definition, Formula, and Example
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.
What is Stuff+?
Stuff+ is a machine-learning model that grades a pitch's raw quality based purely on its physical characteristics — velocity, spin rate, horizontal and vertical movement, release point, and extension — without caring whether the pitch produced a swing, a whiff, or a home run. It answers one question: how nasty is the pitch itself? The scale is normalized so 100 equals league average and 10 points equals one standard deviation. A 110 pitch is above average, 120 is plus, and anything above 130 is elite Cy Young material.
How Stuff+ is calculated
Stuff+ models — the public versions from FanGraphs (Eno Sarris, Max Bay), PitchingBot, and Cameron Grove's model — are all built the same way. A gradient-boosted tree (usually XGBoost) is trained on millions of pitches of Statcast data to predict the expected run value of a pitch from its physical inputs alone: release velocity, spin rate, spin axis, horizontal break, induced vertical break, release height, release side, and extension. Each pitch type is modeled separately so a curveball is judged against curveballs, not fastballs. The model's predicted run value is then normalized:
Stuff+ = 100 + 10 × ((league-mean xRV − pitch xRV) / league-SD xRV)
Lower expected run value is better for the pitcher, which is why the sign flips. Command, sequencing, and outcomes are deliberately excluded — that's Location+'s job. The two combine into Pitching+.
Worked example: Spencer Strider's fastball
In 2023, Spencer Strider's four-seam fastball registered a Stuff+ of roughly 125 at FanGraphs, top five in MLB. The ingredients: 98.2 mph average velocity, 2,440 rpm spin, 17 inches of induced vertical break, and 6.9 feet of extension — meaning it effectively plays like 99+ mph out of the hand. Compare to Mason Miller's fastball (Stuff+ ~133 in 2024 on 100+ mph and 19 inches of ride), or Brandon Woodruff's pre-injury slider (~130). On the other end, command-first starters like Miles Mikolas sit around 85-90 Stuff+ with below-average raw ingredients.
Why Stuff+ matters
Stuff+ is front-office gold because it stabilizes faster than ERA or FIP. A pitcher's Stuff+ is meaningful after a few hundred pitches, while ERA needs 150+ innings. Teams use it to spot breakout candidates before results catch up — the Dodgers, Guardians, and Rays all run internal stuff models and explicitly coach pitchers toward shapes their model likes. Fantasy managers use Stuff+ to front-run strikeout-rate jumps. Scouts use it as a sanity check on velocity-biased eyeball reports.
Limitations and common misconceptions
Stuff+ says nothing about command. A 125 Stuff+ fastball thrown down the middle still gets hit 500 feet. That's what Location+ measures, and Pitching+ combines the two. Different public models also disagree — FanGraphs Stuff+, PitchingBot, and Cameron Grove's Stuff+ can produce double-digit gaps for the same pitcher because they weight inputs differently. Stuff+ also doesn't factor in pitch sequencing, so a pitcher whose fastball plays up off his changeup won't get credit for the tunneling effect. Treat it as one input, not a verdict.
Related terms
In Legends Deck
Legends Deck uses Stuff+ as one of the inputs into each pitcher card's "Stuff" rating, which drives per-pitch whiff probability and weak-contact rates in the simulation engine. A starter with a 130 Stuff+ four-seamer gets a meaningfully higher swing-and-miss curve than one at 95, even if their career ERAs look similar — that's how the card captures a breakout pitcher before the traditional stats catch up. Pair it with a high Location+ grade and you get a deck-defining ace.