BABIP, or batting average on balls in play, measures how often a batted ball that stays in the park falls for a hit. It leaves out home runs, strikeouts and walks, so it isolates what happens once the ball is put in play. The league average sits right around .300 almost every season, which is why a hitter or pitcher far above or below that mark is often due to regress.
What Drives BABIP
| Factor | Effect on BABIP |
|---|---|
| Line drives | Raise it the most; line drives fall for hits far more often than grounders or fly balls |
| Speed | Fast runners beat out more infield grounders |
| Ground balls | Land for hits more often than fly balls that stay in the park |
| Pop ups | Almost always outs, so they drag BABIP down |
| Defense | A strong defense behind a pitcher lowers the BABIP he allows |
| Luck | Seeing eye grounders and bloops add up over short stretches |
How to Use It
BABIP is a luck detector. When a hitter posts a .380 BABIP in April with no change in his contact quality, expect his average to fall. When a pitcher allows a .240 BABIP, his ERA is probably flattering him, which is why analysts pair BABIP with FIP. Hitters who consistently run high BABIPs year after year usually earn it with speed and line drive swings.
Example
A hitter with 150 hits, 25 home runs, 550 at bats, 120 strikeouts and 5 sacrifice flies has a BABIP of 125 divided by 410, or .305, right at league average.
Related
What is FIP · What is wRC+ · What is OPS · What is WAR
Definitions from the FanGraphs Sabermetrics Library.