BABIP and xBABIP differences


BABIP, or Batting Average on Balls In Play, is becoming a common tool in analyzing hitters over short spurts of time.  If a player has a .450 BABIP for a month, most people know that such success cannot be sustained due to luck.  Extreme cases are easy to evaluate, but a player with a .250 or .350 BABIP is not near league average (.290-.300), yet could not be lucky/unlucky.  Using batted ball profiles, one can determine an expected BABIP (xBABIP) to see if the hitter has over or under-performed.

The main components in my xBABIP model are line drives (LD%), ground balls (GB%), popups (IF/FB%), home runs (HR/FB%), strikeouts (K%), and Speed score.  Line drives are the most important factor, since they have such a high BABIP.  More line drives mean a higher BABIP.  Groundballs have a higher BABIP than flyballs, so a higher GB% means a slightly higher BABIP.  Popups are almost automatic outs, so these have a negative correlation with BABIP.  Since flyballs have such a low BABIP, the higher percentage of those that go out of the park lessens the negative effect on BABIP.  A higher K rate increases BABIP a bit, since it’s assumed that a hitter is swinging, and hitting the ball, harder which increases K’s but also helps BABIP.  Speed has a small effect on groundballs.

Here are the Braves hitters and their BABIPs and xBABIPs.

BABIP xBABIP
McCann 0.287 0.267
Freeman 0.339 0.327
Uggla 0.253 0.281
Gonzalez 0.285 0.283
Jones 0.295 0.292
Prado 0.266 0.269
Bourn 0.369 0.364
Heyward 0.260 0.273

As you can see, Uggla was fairly unlucky and Heyward had some bad luck.  McCann was pretty lucky and Freeman was a bit fortunate.  To show how much of an effect BABIP can have on results, Uggla’s .233/.311/.453 turns into a .253/.329/.473 slashline, maybe even better if a couple doubles could be added.  While past luck is good, the most important thing is projecting future batted ball profiles.  It does not make sense to use Bourn’s .364 xBABIP for this year, since it’s unlikely he can match the 26.6% line drive rate, which was 6% higher than his previous career high.

My quick calculator is nowhere near the best possible model, since it does not factor in linked skills.  A fast player should get a bit more of an advantage having a higher GB%.  A hitter with a high HR/FB% should get less of a penalty for hitting more flyballs.  I just wanted to show how much of a factor luck can play in hitting.  These differences are completely unpredictable, but knowing the base skillset makes for the best projection.

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  • Big Bad Bob

    I am not a well versed in the advanced metrics as I should be, but having played and watched baseball for over 50 years, I do not think that BABIP or xBABIP is consistent enough to measure the ability or luck of a player. I believe that “luck” is the primary facet of hitting.
    For example, does BABIP consider a weak flare to Centerfield to be purely luck, or skill? If it is “luck”, then should it be excluded as a hit, but entered as luck? Further, a line drive could be caught or missed by inches. Does it mean that if a line drive is inches from the fielder’s glove that it was luck or skill? Was it the hitter’s skillset to hit line drives inches away from the fielder’s range? Also, what if a player has an inordinate number of weak singles one year and line drives the next year, but hovers near the same batting average and number of hits each year? Was he lucky one year and unlucky the next or do the number of hits make his BABIP appear the same?
    I know that a lot of statheads will critisize my lack of understanding of the new metrics, but I think that I can watch a player for a couple of years and determine whether that player is lucky or good. That won’t work if you are in the baseball business, because no team has 1000 scouts to watch 1000 players.
    Perhaps, I’m too old to grasp the idea behind the stats…perhaps, I’m to old to understand what usefulness it holds for the normal baseball fan. After all, luck is a part of the game. And, truth be told, sometimes it’s better to be lucky than good.
    Ask Francisco Cabrera!

  • leetro

     @Big Bad Bob Luck does play a huge role in individual games, but over a full season, it evens out pretty well.  The difference between the two figures are rarely more than 50 points.I can answer your question about the ducksnorts one year and line drives the next.  BABIP would see those as the same year, but xBABIP would see them different.  The line drives would increase xBABIP, while the weak singles would decrease it.
     
    The main thing that the stats are intended for is future projections.  xBABIP gives us a baseline for what the hitter’s BABIP should be, and that is all we can hope for, since BABIP is the most volatile stat in the game.

  • Big Bad Bob

    Thanks for your answer, leetro.
    As I said, perhaps I’m too old for the new advanced metrics.
    There is no way to precisely predict the future, as we all know, but can’t someone who has followed a player’s career predict that player’s norm?
    For instance, Mickey Mantle had a career year in 1956 winning the Triple Crown, batting .353 and hitting 52 homers. Everyone knew (or should have known) that it was unsustainable. The next year, he hit .365 with 34 homers. The next year he batted .304 with 42 homers. (I know that homers aren’t included in BABIP, I just love Mantle!)
    In other words, for 2 years he was lucky with his batting average. He regressed to the mean after that 2 year stretch. Everyone knew that he wouldn’t hit .350 or better because he loved to swing for the fences, so much.
    BABIP wasn’t around then, but everyone knew he got lucky.
    For a fan that watches 150 games a year, BABIP is unnecessary because we know if “our” players are lucky or not. We also know their capabilities.
    I guess it’s a stat that one can use to evaluate players with which one is unfamiliar. That’s all I would use it for.

  • leetro

    You’re close to the point.  Having a BABIP higher than normal doesn’t necessarily mean he was lucky.  With Bourn’s case, he was legitimately hitting the ball better, so it wasn’t luck that brought him to a .369 BABIP.  He isn’t likely to sustain such a high LD%, but I wouldn’t call him lucky for hitting all of those line drives.  I only call someone lucky if their BABIP is much higher than his xBABIP.

  • aryanspecial

    Francisco Cabrera. Luckiest moment of all time. He should’ve received double points….
    I’m only 32 and aren’t completely in on the advanced stats, but the numbers look about right to me. Again, Bourn’s numbers on top. I think we underestimate what he can bring in a contract year.