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Posted By Jeff Zimmerman On September 26, 2011 @ 4:15 pm In Meta Analysis | 15 Comments
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.
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).
The following is a procedure for downloading and using the spreadsheet. First download the spreadsheet from Google Docs by going to File, Download As and select the desired format (don’t select .csv). Open the spreadsheet in Excel or OpenOffice (they are the only two formats I verified). Next, go to a hitter’s Batted Ball data (like Dustin Pedroia). Select and copy all the yearly data (some funkiness happens with the career data).
Finally, open the downloaded spreadsheet and Paste the copied data into the spreadsheet (select/highlight the Yellow box that designates the first year before pasting).That is it. The xBABIP values will be automatically generated.
A players xBABIP will be calculated without having to hand enter every number. Hopefully you find the information useful and let me know if you have any questions.
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