More than anything else, BABiP decides baseball games. It's an extraordinarily powerful force, and it's not extraordinarily well understood, even among the sabermetric crowd. In terms of concepts, it falls somewhere between dark matter and the great white whale. Once someone fully explains BABiP, we'll probably just pack up all the spreadsheets and scientific calculators and slide rules, because the grand unifying theory of baseball will have its keystone.
It's kind of a big deal, is what I'm saying.
So what is BABiP?
Batting Average on Balls in Play (BABiP) is simply the rate at which balls turn into hits instead of outs upon entering the field of play. If you want to figure BABiP yourself, simply subtract a player's home runs from his hit total, and divide that number by at-bats, minus strikeouts & homers, adding sacrifice flies. Or, you could just look at the player's BABiP line on Fangraphs or Baseball-Reference, whichever you prefer.
So, how do I use BABiP?
BABiP league-wide tends to average around .300, which means that just about thirty percent of all balls hit turn into hits, and about 70 per cent turn into outs. There's a fluctuation among players, though; a fast player who hits the ball on the ground a lot (eg, Ichiro at .344) hold to a higher BABiP than a slower, more powerful guy who's trying to get the ball in the air and over fences (Adam Dunn is a career .286). Likewise, a groundball pitcher is going to have a different BABiP (Derek Lowe at .297) than a flyball-heavy pitcher (Ted Lilly's career rate is .270).
So, as a rule of thumb, slide a player's expected future performance one way or another based off his BABiP. Say Mitch Moreland goes crazy over April-May this year, and people start thinking he's turned a corner; until you look at his BABiP over that stretch and see it's .375. His career mark is .281, so you can imagine that's going to slide downward toward his career mark over the longer period. Fewer balls fall in, and more turn into outs, and his average slides accordingly.
The rule of thumb to remember is to regress toward either the league average (for players we don't have a significant career sample for) or the player's career average, to have a hint towards what his future is going to look like.
So what does BABiP say about the 2014 Texas Rangers?
One of the strengths of the Rangers between 2011 and 2012 was Matt Harrison and his quiet, steady production. The was missing last year, which was obvious as the team ran about forty five players through the rotation, most of which would end up playing defensive tackle for the Cowboys in the fall.
BABiP is a key thing for Harrison, since stylistically he's bent towards weak contact and forcing batters to drive the ball into the ground. When Harrison began establishing himself, his BABiP went from over .300 to .284. one of the first indicators whether Harry is “back” or not will be his BABiP. If he's getting a lot of groundballs, and those groundballs are getting gobbled up by Beltre, Andrus and Profar, it'll be low. If he's hitting too much of the plate and allowing liners, it'll look high.
The common shorthand for BABiP is luck; in that a hitter with a high BABiP is viewed as lucky, or a pitcher with a high BABiP is viewed as unlucky. That's not a dismissal of a player's effort; it's simply that if a player could have more of his contacted balls drop in, he would (look at Crash Davis' rant about his batting average in Bull Durham). Likewise, if pitchers had complete control over whether balls hit off them turned into outs or hits, they'd go for outs. So we can assume that variations in BABiP are the result of factors outside the player's direct control (facing better or worse defenses, playing in a large ballpark versus a small one, etc), therefore 'luck' is just a catch-all term.
Plus, as I said before, our understanding of BABiP as a phenomenon is incomplete right now. As metrics and tracking technologies like Field F/X advance and expand, hopefully it's something we'll have a better handle on, and can explain with a better term than luck.
Joseph Ursery spends an unreasonable time comparing line drive rates on Fangraphs, so this article was a special labor of love for him. For more thoughts on BABIP or craft beer, follow him on Twitter at @thejoeursery.