Definitions

# Batting average on balls in play

In baseball statistics, Batting average on balls in play (abbreviated BABIP) is a statistic measuring the percentage of plate appearances ending with a batted ball in play (excluding home runs) for which the batter is credited with a hit BABIP is commonly used as a red flag in sabermetric analysis, as a consistently high or low BABIP is hard to maintain - much more so for pitchers than hitters. Therefore, BABIP can be used to spot fluky seasons by pitchers, as those whose BABIPs are extremely high can often be expected to improve in the following season, and those pitchers whose BABIPs are extremely low can often be expected to regress in the following season. The formula for BABIP is:

$BABIP = frac\left\{H-HR\right\}\left\{AB-K-HR+SF\right\}$

where H is hits, HR is home runs, AB is at bats, K is strikeouts, and SF is sacrifice flies.