Batting Average on Balls in Play (BABIP) is actually a pretty tried and true part of the baseball vernacular. Sabermetricians may have given it a long name with a fun-sounding acronym, but the principle goes back as far as presidential first pitches and wooden bats. Everyone knows that bloop hits and seeing eye ground balls go for hits quite regularly and that screaming rockets get snatched out of the air by leaping defenders pretty often. You couldn’t find a baseball fan alive who would argue with you on that simple fact.
BABIP is really just the amalgamation of all of those screaming rockets and bouncing grounders. When a batter puts the ball in play, it either goes for a hit or it doesn’t. Sometimes it’s a clean single, sometimes the defender can’t quite reach it. It’s a game of inches and these things happen.
Yet there is another axiom of baseball, one that’s less tried and true, that says these screaming liners that are caught and bloops that find some grass even out. This simply isn’t true, and it especially isn’t true over the course of a few months or even an entire season. Sure, over the course of six years, the number of hard hit balls that get caught and weak grounders that find a hole will balance out, but we don’t judge players in 3,500 plate appearance samples. We judge players based on individual seasons and those lucky moments can really swing the number of hits you rack up or allow.
Let’s walk through a basic example. We’ll even use batting average to make it really simple. Let’s say you come to the plate 600 times, if you have an 8% walk rate, you’ll walk 48 times and if you have a 20% strikeout rate you’ll punch out 120 times. Let’s say you hit 22 HR and don’t get involved in any silly sacrifices, you don’t get hit, or do anything else unusual. That leaves you with 410 balls put into play. The average player will get 123 hits (assuming a .300 BABIP) on those 410 balls in play and will wind up with a .262 batting average.
Now let’s assume that this player got 20 more hits. That wouldn’t even be one extra hit per week and let’s say it’s because the he hit a few bloops that fell in. One extra bloop hit every eight games. That’s a .299 batting average for the season. Less than one hit a week turns you from a .260 hitter to a .300 hitter. The impact of a few extra balls that get through the infield could really make a difference.
And researchers have shown that while certain hitters are capable of running higher BABIPs than others, luck and defense still impact a given hitter’s or pitcher’s results. Miguel Cabrera hits the ball harder than most of the league, so it’s not surprising that more of his balls in play go for hits, but he could easily have 15 or 20 of those balls in play get grabbed or dropped completely due to random chance.
That’s a hard thing for people to accept in the aggregate. We don’t like to accept that randomness plays such a big role in our lives. Cabrera is going to get more hits that most of the league because he’s better than they are, but he’s never going to hit exactly to his true talent level either because weird stuff happens in baseball. Balls take funny hops. Fielders take one step to the left instead of taking one to the right. The ball just happens to find the one lane where no one can reach it even though it was hit at 35 miles per hour.
You’ve seen this happen a million times. It’s baseball. And the evidence indicates that these types of hard luck (or good luck) plays do not even out until you get into multiple years of data for both hitters and pitchers.
A few hits can make a big difference in a player’s stat line, whether they’re a pitcher or a hitter and it’s easy to remember a couple dozen luck-influenced moments for every player each season. Sometimes they even out, but sometimes they don’t.
This is why BABIP matters.
BABIP let’s us see how often a ball falls for a hit when it’s put into play. On average that will happen 30% of the time, but even the best hitters can only shift that to 35% of the time. But the secret is that while hitters will converge on their true talent marks in the long run, the amount the defense and luck play a role in the short run is immense. And even if you don’t want to believe it, a season is a small sample of data in this regard. If you’ve been watching a player run a .320 BABIP for years and this year they’re “breaking out” but have a .370 BABIP, they’re probably just getting lucky.
Let’s consider a couple examples. First, this is the type of play that the Inside Edge system would probably call a remote play, meaning that it gets turned into an out about 1-10% of the time. So when you’re a hitter, this is essentially the kind of swing that should lead to a hit. Whoops.
And now let’s look at this play, which you could easily call routine. It’s the kind of play that should almost never go for a hit. It might look tough but the ball is only about two steps to his left. You can see briefly how upset Dustin Pedroia is.
These aren’t cherry-picked examples, these are just two plays I grabbed almost at random. There have been more than 200 plays this year, according to Inside Edge, in which the batter could reasonably expect to get a hit 90% of the time or more, but a fielder made a play. That probably doesn’t sound like much, but this is just one small slice of the pie. On the other side, there have been something like 1,000 routine plays that have turned into hits.
This is just a simple estimate, but it points to a key concept. Defense and luck play a role in determining if a ball goes for a hit. It’s not just about the batter and the pitcher. We typically want to isolate performance and BABIP can help us do that by showing us who might be the beneficiary of good luck or bad defense.
This is an easy to accept notion at the individual level. Just go watch those two plays again. The next step is to recognize that it can take a while for those types of plays to even out, which means that every players’ numbers aren’t 100% theirs. They’re responsible for a lot of what happens on the field, but some is just outside their control and good analysts try to determine just how much that is.
Think about a ground ball pitcher in front of a bad defense and then think about him in front of an amazing one. He’ll allow fewer hits in front of the good defense and probably fewer runs as a result. Was he a different pitcher? No. Luck works the same way, but it’s even harder for us to observe. We know when a defender is bad, but we don’t know when luck might strike.
As you watch your favorite team over the next week, count how many well hit balls are caught and how many weak ones fall for hits. Think about the number of games that could influence over a full season and then think about why we care about BABIP.
Have BABIP questions? Ask them in the comments!
Neil Weinberg is the Site Educator at FanGraphs and can be found writing enthusiastically about the Detroit Tigers at New English D. Follow and interact with him on Twitter @NeilWeinberg44.