What is BABIP?
BABIP, or batting average on balls in play, was originally designed to measure a pitcher's ability to prevent hits on balls in play.
Today it's widely used to evaluate both pitchers and hitters, and it's a calculation of a hitter's batting average -- or pitcher's batting average allowed -- on batted balls put into the field of play.
That means walks and strikeouts don't count; those aren't batted balls. Nor do home runs; those don't land within the field of play.
The formula: Hits minus home runs, divided by at-bats minus home runs minus strikeouts plus sacrifice flies (H - HR)/(AB - HR - K + SF).
The average BABIP for a major league pitcher or hitter is usually between .290 and.300 and it is often thought that if a player has a higher or lower BABIP than this number, that he’s experiencing good luck or bad luck on his balls in play.
This isn’t necessarily so. A player’s BABIP is also reflective of his ..
Speed-- A fast hitter will likely have a higher BABIP than a slow hitter, because he’ll reach base more often when he hits the ball on the ground.
Quality of contact -- A hitter who hits a lot of line drives, or a pitcher who gives up a lot of line drives will have a higher BABIP than those who don’t.
Defense-- A pitcher with a good defense behind him will have a lower BABIP than a pitcher with a bad defense behind him. Good defense’s will turn a higher percentage of batted balls into outs than the average team.
For a more extensive description of BABIP, click here for Tristan Cockcroft's 2010 primer, from which the information above was provided