- FanGraphs Fantasy Baseball - http://www.fangraphs.com/fantasy -

Here at Rotographs, it is brought up quite often that a player’s xBABIP and BABIP don’t agree. With the help of slash12, I have created a quick and easy method of calculating a hitter’s xBABIP. I have a downloadable spreadsheet that takes the batted ball data and calculates a xBABIP.

While others have created other xBABIP formulas, I find the one from slash12 (originally published at Beyond the Boxscore) to be the most accurate.

xBABIP = 0.392 + (LD% x 0.287709436) + ((GB% – (GB% * IFH%)) x -0.152 ) + ((FB% – (FB% x HR/FB%) – (FB% x IFFB%)) x -0.188) + ((IFFB% * FB%) x -0.835) + ((IFH% * GB%) x 0.500)

Here is a description of the formula’s creation and usage from slash12 in his own words:

This xBABIP formula was something I developed to provide an easy way to estimate a batters BABIP given his batted ball percentages as they appear on Fangraphs. I did this by doing a linear regression on the batted ball percentages against historic batted ball data. I’ve found that it has a very high correlation with a batters current year BABIP, however, sample sizes need to be considered as with everything else. Given the fickle nature of BABIP in general, it’s recommended you keep in mind a batters historic BABIP as well. A career .300 BABIP hitter isn’t likely to be a true .360 BABIP hitter, even if his batted ball data says that he is over the course of a partial season.

Here are a couple simple examples where this equation is useful:

Player X 2010: .300 xBABIP .290 BABIP
Player X 2011(April->June) .307 xBABIP .220 BABIP

Here, xBABIP helps reassure us, that Player X is most likely the same hitter he’s always been, he’s just been having some bad luck.

Player Y Career: .330 xBABIP .340 BABIP
Player Y 2010: .370 xBABIP .390 BABIP
Player Y 2011(April->June) .372 xBABIP .380 BABIP

Player Y may have indeed changed his approach in 2010, and 2011 in such a way that his hitting for higher BABIP is legit (perhaps he’s gained bat speed, or a previous injury has finally healed).