Batting average on balls in play (BABIP)

Batting average on balls in play measures how often a ball that stays in the field of play, excluding home runs and strikeouts, falls for a hit. It isolates the part of a hitting outcome most influenced by defense, positioning and chance, from the parts a batter or pitcher controls more directly.

The formula is BABIP = (H − HR) / (AB − K − HR + SF). League-average BABIP for hitters typically sits in the high .280s to low .300s, with meaningful variation by player based on speed, batted-ball quality and home park. A hitter or pitcher whose BABIP is far above or below their own established norm is often experiencing a temporary run of luck that tends to move back toward that norm, an application of regression to the mean.

BABIP is used heavily in evaluating pitchers, where it helps separate pitching skill, captured better by fielding independent pitching, from defense and variance behind them, and in flagging hitters whose hot or cold streak may not be sustainable. The common pitfall is assuming every player's BABIP should regress to the same league-average number; players with elite bat-to-ball skill, speed, or a tendency to hit the ball hard, such as those with high sustained exit velocity, can carry a persistently different true-talent BABIP than average.