Batting Average on Balls In Play (BABIP) measures how many balls in play against a pitcher go for hits. While typically around 30% of all balls in play fall for hits, there are three main variables that can affect BABIP rates for individual players:
a) Defense - Say a player cracks a hard line drive down the third base line. If an elite fielder is playing at third, they may make a play on it and throw the runner out. However, if there’s a dud over there with limited range, the ball could just as easily fly by for a hit. Pitchers have no control over the defenses behind them; all they can do is minimally affect if a ball is more likely to be in the air or on the ground.
b) Luck - Sometimes, even against a great defense, bloop hits can fall in. A batter may turn a nasty pitch into a dribbler that just sneaks past the first baseman, or they may blast a shot in the gap that a fielder makes a diving catch on. A pitcher can make the absolute perfect pitch against a batter, yet the hitter could still dribble it up the middle for a hit. That’s just the game.
c) Changes in Talent Level - Over the course of a season, players can go through periods of adjustment. Maybe a pitcher starts tipping one of their pitchers, their mechanics are off, or they start leaving too many balls over the plate. Balls get hit harder until the pitcher makes the necessary adjustments, but until then, the harder a ball is struck, the more likely it is to fall in for a hit.
Due to all these reasons, BABIP is inherently flaky and prone to variation, which can dramatically affect a pitcher’s hits allowed and ERA. If very few balls in play fall for hits, a pitcher won’t allow many runs to score and will have a very low ERA; similarly, if too many balls fall in for hits, a pitcher’s ERA can skyrockets upward.
If a pitcher has a very high or very low BABIP, it means that whatever the reason for the spike (whether it’s defense, luck, or slight skill changes), that player will regress back toward their career BABIP rate. BABIP rates are flaky and prone to vary wildly from year to year, so we should always take any extreme BABIP rates with a grain of salt.
The average BABIP for pitchers is around .290 to .300, and pitchers have much less control over their BABIP than batters. To what degree pitchers can influence their BABIPs is still up for debate, but it has been proven that pitchers with high strikeout rates tend to generate weaker contact and, therefore, allow fewer hits on balls in play. The same is generally true of relievers, as they can dial up the intensity over shorter outings.
Even then, though, high strikeout pitchers still have career BABIPs just slightly lower than the typical .290 to .300 range. Think Justin Verlander (.285 career BABIP) or Clayton Kershaw (.279 career BABIP).
And if any pitcher is posting an extremely deviant BABIP, expect them to regress toward league average.
Things to Remember:
● Saying a player will regress to league average is a tricky subject. See regression for more info.
● Groundball pitchers have a lower BABIP on groundballs than other pitchers. In other words, if a pitcher has an extreme groundball rate, they also tend to be extra good at making sure those grounders are hit weakly and turn into out.
Links for Further Reading: