What is xBA? Definition, Formula, and Example
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.
What is xBA?
xBA, short for expected batting average, is a Statcast metric that predicts batting average from the physical quality of contact rather than from where the ball actually landed. Every batted ball gets a hit probability between 0.000 and 1.000 based on how often balls with similar exit velocity and launch angle became hits historically; xBA is the sum of those probabilities divided by at-bats, with strikeouts counted as outs (probability 0.000). It answers the question, "Given how hard and at what angle this hitter struck the ball, what should his batting average be?"
How xBA Is Calculated
For each batted ball, Statcast looks up its hit probability from a model built on every tracked batted ball since 2015. The model uses:
1. Exit velocity (mph off the bat)
2. Launch angle (vertical angle off the bat)
3. Sprint speed — only for weakly hit topped ground balls, where a speedster like Jose Altuve genuinely beats out more of them
The formula is:
xBA = (Σ hit probability of each batted ball + 0 × strikeouts) / (AB)
Home runs get probability 1.000. A 107 mph line drive at 15 degrees might carry a 0.920 probability. A 78 mph popup at 60 degrees drops to 0.020. Strikeouts enter the denominator as zero-probability events, which is why high-strikeout hitters can't paper over whiffs with loud contact.
Worked Example
In 2023, Luis Arraez hit .354 with an xBA of .326 — he outperformed his expected mark by 28 points, partly because he places the ball through infield holes better than anyone in baseball and partly because he runs about average, so weak grounders that the model calls outs sometimes find grass. Aaron Judge in 2024 hit .322 with an xBA around .289, meaning even his monstrous raw numbers were slightly flattered by BABIP luck. On the other end, Christian Yelich posted seasons where his xBA sat 30+ points above his actual BA — Statcast said he was hitting into bad luck, and the following year his surface numbers rebounded.
Why xBA Matters
xBA strips out two big sources of variance: defensive alignment and batted-ball luck. Front offices use it as a leading indicator — a hitter whose BA is 40 points below xBA is a regression-to-the-mean buy target, and one whose BA sits 40 points above xBA is a sell candidate.
DFS and season-long fantasy players use xBA to find hitters whose surface stats don't yet reflect their actual contact quality. It's also the basis for xwOBA, which extends the same modeling approach to full offensive value.
Limitations and Common Misconceptions
xBA does not know about pitch location, count, or pitch type — a 95 mph line drive gets the same probability whether it came on a 3-0 cookie or on a two-strike back-foot slider. It also doesn't model defensive shifts directly; with the 2023 shift ban, the gap between xBA and actual BA has narrowed for pull-heavy left-handed hitters, but players who still see defensive tilts (e.g., some pull-heavy righties facing modern fielder positioning) can chronically underperform.
It's sometimes confused with BABIP, which uses actual outcomes on balls in play; xBA uses modeled outcomes and includes home runs and strikeouts. A hitter can have normal BABIP and still be wildly over- or underperforming xBA if the directional placement of their balls is unusual.
Related Terms
In Legends Deck
Legends Deck uses the delta between xBA and actual BA to calibrate Luck Adjustment on hitter cards. A player with a .280 BA and .305 xBA receives a slight upward nudge on contact-rate rolls, reflecting that his underlying contact quality outpaced his results. This keeps cards tied to repeatable skill rather than to season-long BABIP swings, so the 2023 version of Yandy Diaz (who overperformed xBA) and the 2024 version (who regressed) rate differently than their triple-slash lines alone would suggest.