In baseball statistics, batting average against (denoted by BAA or AVG), also known as opponents' batting average (denoted by OBA),^[a] is a statistic that measures a pitcher's ability to prevent hits during official at bats. It can alternatively be described as the league's hitters' combined batting average against the pitcher.

Batting average against is calculated as:^[2]

${\displaystyle BAA={\frac {H}{BF-BB-HBP-SH-SF-CINT}}}$

for which:

• H is the number of hits allowed by the pitcher
• BF is the number of batters faced
• BB is the number of base on balls
• HBP is the number of hit batsmen
• SH is the number of sacrifice hits
• SF is the number of sacrifice flies
• CINT is the number of catcher's interference

For example, if a pitcher faced 125 batters and allowed 25 hits, issued 8 walks, hit 1 batsman, allowed 2 sacrifice hits, allowed 3 sacrifice flies, and had 1 instance of catcher's interference, the pitcher's BAA would be calculated as:

${\displaystyle BAA={\frac {25}{125-8-1-2-3-1}}={\frac {25}{110}}=.227}$

Reference site Baseball-Reference.com more simply defines BAA as hits divided by at bats, as "at bats" for a pitcher equates to the above noted denominator (batters faced less walks, hit by pitch, sacrifice hits, sacrifice flies, and catcher's interference):^[3][b]

${\displaystyle BAA={\frac {H}{AB}}}$

For example, in 2021, Max Scherzer had the best (lowest) batting average against in Major League Baseball among qualified pitchers.^[3][c] Scherzer's BAA for the 2021 season was:^[3]

${\displaystyle BAA={\frac {H}{AB}}={\frac {119}{644}}=.185}$

• Hits per nine innings (H/9)
• Walks plus hits per inning pitched (WHIP)

• OBA Calculator at captaincalculator.com

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