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What Batting Average Against Is
Batting average against (BAA, sometimes written AVG or OAV) is the batting average that opposing hitters produce against a given pitcher. It answers a simple question: when a batter completes an at-bat against this pitcher, how often does he get a hit? A pitcher with a .200 BAA holds hitters to a Mendoza-line offense; a pitcher allowing .280 is getting squared up like a league-average bat against everyone. It is the pitcher's-eye-view mirror of a hitter's batting average.
How Batting Average Against Is Calculated
The formula is hits allowed divided by at-bats faced:
BAA = Hits Allowed / At-Bats Against
The subtlety is the denominator. At-bats against is not the same as batters faced. You compute it by removing outcomes that do not count as at-bats:
At-Bats Against = Batters Faced − Walks − Hit-By-Pitch − Sacrifice Flies − Sacrifice Hits − Catcher's Interference
So a pitcher who walks many batters can post a deceptively low BAA, because walks shrink the at-bat pool without adding hits. This is why BAA must be read alongside WHIP, which does count walks.
Worked Example
The single-season record is Pedro Martínez in 2000, who held hitters to a .167 batting average — the lowest qualified BAA in modern history, during one of the highest-offense seasons ever. If a pitcher allows 120 hits over a season in which he faces 750 batters with 60 walks, 5 hit-by-pitches, 5 sacrifice flies, and 0 sacrifice hits, his at-bats against equal 750 − 60 − 5 − 5 − 0 = 680, and his BAA is 120 / 680 = .176. By contrast, a back-end starter allowing 180 hits in 700 at-bats faced posts 180 / 700 = .257.
Why It Matters
BAA is an intuitive, broadcast-friendly measure of how hittable a pitcher is, and it correlates with run prevention. Front offices and fantasy managers use it as a quick screen for dominance, especially for relievers whose small samples make ERA noisy. A reliever with a sub-.200 BAA and a high strikeout rate is missing barrels and missing bats — a profile that holds up in high-leverage spots.
Limitations and Misconceptions
BAA inherits all of batting average's blind spots and adds a few. It ignores walks entirely, so a wild pitcher can hide behind a tidy BAA. It treats a single and a home run identically, telling you nothing about the damage on contact — opponents' slugging or OPS does that. And like BABIP, BAA is heavily influenced by defense and luck on balls in play; a low BAA backed by a weak strikeout rate often regresses upward. For these reasons, modern analysts lean on FIP, xERA, and expected batting average (xBA) for predictive value, treating BAA as a descriptive snapshot rather than a forecast.
Related Terms
In Legends Deck, a pitcher card's contact-suppression rating is anchored to BAA and its expected-stat cousins: cards that historically held low batting averages against generate more soft contact and fewer base hits in the simulation. Because the engine also tracks walks separately, a low-BAA, high-walk card plays exactly like its real counterpart — hard to hit, but prone to traffic on the bases.
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