BABIP: What Do We Know?
by Steve Slowinski on Dec 16, 2010 2:00 PM EST
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PrintThis article is another in BtB's ongoing Saber Ed discussion. For previous articles, including an interview with ESPN's Mark Simon, see these links: Intro, Defining Saber, Simon Interview 1, Simon Interview 2.
To be able to teach a concept to someone else, you first have to understand it yourself. That seems like such an obvious statement, but on numerous occasions, I've tried to explain an idea that I thought I knew well, only to find myself stumbling and backtracking my way through the conversation. To teach something well, you not only have to understand it, you have to know it forward and backward.
That brings me to today's subject: Batting Average on Balls In Play (BABIP). BABIP, as we all know, is one of the more important sabermetrics statistics. It's a deceptively simple statistic - hits divided by total balls in play, excluding homeruns - but explaining its implications gets difficult. To understand BABIP, you need to also understand sabermetrics concepts like DIPS theory and statistic concepts like random variation, and our understanding of BABIP is changing all the time. It's a nuanced statistic, and those nuances get glossed over or missed in many analyses and descriptions.
With those nuances in mind, here's my question for this week: what's our current understanding of BABIP? What are all the nuanced caveats? Or in other words, if you wanted to describe BABIP to a saber-newbie, how would you do so? There's research being done all the time on DIPS theory and BABIP, and while I feel fairly confident in my current understanding of BABIP, I'm also certain there are nuances I'm missing - nuances many of us are missing.
After the jump, I'll get the conversation started with some of my own interpretation of BABIP. There are many people reading this out there that are far, far smarter than I am, so please, be gentle.
The Basics
- BABIP can dramatically affect a hitter's batting average or a pitcher's ERA. If a large number of a hitter's balls in play go for hits, that can boost his batting average quite high. Also, if a pitcher lets up a large number of balls in play, he'll have a higher number of baserunners and will be more likely to let in runs.
- That said, BABIP is an inherently fluky statistic, with little year-to-year correlation. That means that if a pitcher has a .370 BABIP one season, it's not a given that they'll post a similar rate the next season.
- To estimate what a player's expected BABIP should be going forward, you should look at the player's career BABIP rates (assuming they've had three season or more in the majors) and use that for a baseline. League-average BABIP rates are normally around .290-.310, but certain players may have career rates slightly lower or higher than that. If a player hasn't had more than three seasons in the majors, it's best to estimate their expected BABIP as league-average.
- EDIT: Batters have way more control over their BABIP rates than pitchers (h/t Dan Turk). I should have made this point clearer initially, but when estimating a player's future BABIP, you should be sure to regress pitcher's BABIP rates much more. They're more likely to perform close to league-average, while batters are more likely to perform closer to their career average.
- Why do players over- or under-perform on single-season BABIP rates? Why does BABIP fluctuate so much? We tend to simplify and call this fluctuation "luck" or "random variation", but I see it as a combination of three influences:
a) Defense - If a pitcher has a collection of stiffs fielding behind him, then he should let up more hits on balls in play than a team with a superior defense. Also, defensive shifts can help or hurt players. As an exaggerated example, a batter that consistently hits into a shift may have a lower BABIP than a typical player.
b) Minute Changes in Talent Level - Over the course of a season, players can go through periods of adjustment (AKA "slumps"). Maybe pitchers adjust to a weakness that a batter has, and the batter starts making less solid contact and getting fewer hits. Maybe a pitcher is off with their mechanics or batters have learned to adjust to certain pitches, and the pitcher leaves more hittable pitches over the plate than normal. The batters make more solid contact, resulting in a higher BABIP for the pitcher.
c) Luck - Sometimes, even with a great defense, bloop hits can fall in. A batter can turn a nasty pitch into a dribbler that just sneaks past the first baseman. Hits can fall in despite the best pitches and the best defenses - that's just the game.
d) Remember: regardless of the reason why a player's BABIP is fluky, they are still likely to regress the following season. Team defenses change, players constantly make adjustments and improve their skill levels, and luck / random variation balances out. - Line drives go for hits more often than
flyballsgroundballs, andflyballsgroundballs go for hits more often thangroundballsflyballs (h/t garik16). - Fast hitters can sustain slightly higher-than-average BABIP rates because of their speed.
- Groundball pitchers have a lower BABIP on groundballs than other pitchers.
- Can certain profiles of pitchers have a better-than-average true talent BABIP?
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"flyballs go for hits more often than groundballs."
Errr, isn’t this backwards unless you’re counting home runs?
Shoot...that's right.
I forgot to fact check that before publishing. Thanks.
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by Steve Slowinski on Dec 16, 2010 2:22 PM EST up reply actions
I think that comes from the fact I automatically think groundballs = awesome.
First instinct.
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by Steve Slowinski on Dec 16, 2010 2:25 PM EST up reply actions
It's also true that BABIP is higher for GBs than FBs
But SLGIP is close to the same because FBs go for extra bases more often.
by Dan Turkenkopf on Dec 16, 2010 2:45 PM EST up reply actions
Where is the line between a fly ball and a line drive?
I would imagine that some fly balls have to be hit pretty hard and therefore are more likely to be hits. Isn’t it possible that some players could hit a whole bunch of borderline LD/FB and end up with a higher BABIP than expected because so many FB are actually close to be line drives?
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by RhodeIslandRoxfan on Dec 16, 2010 2:57 PM EST up reply actions
That's an interesting question
The line between them is pretty blurry.
Your scenario is probably the cause of some of the noise we see in certain cases.
by Dan Turkenkopf on Dec 16, 2010 3:07 PM EST up reply actions
This is correct.
This is one of reasons why certain people (BP’s Colin Wyers, for instance) are heavily distrustful of measures using batted ball types (such as UZR), as the LD/FB distinction is applied differently throughout baseball by the different people tracking them at each ballpark.
It's important to distinguish between batters and pitchers when discussing BABIP
You do a little bit but probably not enough in your first section.
Batters have a great deal more control over their babip than do pitchers and therefore are more consistent from year to year.
I think you’re probably correct about changes in true talent affecting babip but agree it’s hard to measure.
by Dan Turkenkopf on Dec 16, 2010 2:22 PM EST via mobile reply actions
Yes, that's very true. Batters have way more control.
Tried to make that clear, but probably not enough.
And I just saw something on twitter that lines up with this. Relievers are typically .005 better with BABIP…is that true? Don’t think I’d heard that before.
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by Steve Slowinski on Dec 16, 2010 2:24 PM EST up reply actions
I've heard closers tend to have an advantage before
Along with knuckleballers, but never a blanket statement about relievers.
by Dan Turkenkopf on Dec 16, 2010 2:45 PM EST up reply actions
Rule of 17
tango compared the Babip of the RP and SP when then changed positions
http://www.insidethebook.com/ee/index.php/site/comments/starter_v_relief_1953_2008/
- .-. ..- … – / – …. . / .—. .-. - .. . … …
by Jeff Zimmerman on Dec 16, 2010 6:19 PM EST up reply actions
Very interesting
Is that a pretty important result to find (i.e. it deserved more discussion than in that thread)?
I’m assuming it has to do with the correlation between pitch speed and BABIP, although I didn’t necessarily find a substantial jump in average pitch speed when comparing starters and relievers.
by Dan Turkenkopf on Dec 16, 2010 6:33 PM EST up reply actions
Hope that fixed it...tried to make the distinction clear.
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by Steve Slowinski on Dec 16, 2010 2:31 PM EST up reply actions
I've always been interested in how ballparks affect BABIP
and how a player’s BABIP will change when he switches teams because of the ballpark. Is there a list anywhere of the average BABIP in each ballpark over a large sample size?
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by RhodeIslandRoxfan on Dec 16, 2010 2:36 PM EST reply actions
You'd also need to do it by batter handedness
For instance, a left-handed flyball pull hitter in Fenway is probably going to get a boost to his BABIP since what would be home runs in other parks bounce off the wall for a non-HR hit.
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That would be RH pull hitters in Fenway
but you’re right in that it is the most obvious example of ballparks affecting BABIP. The enormous OF in Colorado (and maybe Petco as well) would also be outliers, you’d think.
Is there any correlation between high BABIP and high K%?
On the surface, it makes sense that guys who whiff at the really good pitches (instead of getting fooled into bad contact) and hit the other pitches hard are going to have high BABIPs.
I'm pretty sure there is
Because high BABIP for batters is generally associated with hitting the ball hard, leading to a high slugging on contact (SLGCON as Colin Wyers likes to call it).
If you’re going to have a high K% you better hit really well when you make contact if you want to stay in the majors.
by Dan Turkenkopf on Dec 16, 2010 3:05 PM EST up reply actions
Good points.
Newbie question: is slugging on balls in play actually computed out anywhere, or is it just a term of art?
Not that I'm aware of
It’s pretty easy to calculate though
SLGIP: (H + 2B + 2*3B) / (AB – K – HR)
SLGCON: (H + 2B + 2*3B + 3*HR) / (AB – K) or alternatively (SLG * AB) / (AB – K)
by Dan Turkenkopf on Dec 16, 2010 3:31 PM EST up reply actions
Good stuff Steve
As always. BABIP is one of those topics where if you can make some progress with the non/anti SABR crowd, makes it a ton easier to get onto other concepts.
Rays/Cubs fan - AnotherCubsBlog.net
Exactly. For such a simple stat, I feel like it's a tougher one to explain and sell.
But if you can, everything else follows pretty easily.
I’m always amazed by how much info is hidden in this one stat. It’s crazy.
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by Steve Slowinski on Dec 16, 2010 4:46 PM EST up reply actions
It is a good exercise to really lay down what we know about BABIP
Maybe I’m wrong on this, but sometimes I see stats-oriented people too willing to simply right things off as luck or BABIP variation. While it’s probably mostly true, it comes across that people aren’t willing to at least dig a little deeper on the whole notion.
Rays/Cubs fan - AnotherCubsBlog.net
I actually often wonder if it obscures more than it clarifies
Especially for batters where you really don’t want to remove home runs from the equation.
For pitchers, it’s useful to explain how big a role the defense plays in determining how pitchers do, but I think there’s an over-reliance on BABIP especially for young pitchers who haven’t necessarily established they have major league BABIP “skill”
It’s important to remember that the DIPS concept of a relatively stable league average BABIP only applies to the population of major league pitchers. It’s entirely possible that a pitcher just isn’t good enough on balls in play to stick regardless of his peripherals.
by Dan Turkenkopf on Dec 16, 2010 4:59 PM EST up reply actions
So many good points.
I actually often wonder if it obscures more than it clarifies
I feel like this happens a lot. People look at BABIP and write something off entirely as a fluke, instead of looking at all the possibilities.
James Shields is the example that jumps most to mind for me. Horrible BABIP this season, part of the cause of his horrendous year, but there seemed to be – at least in part – a distinct reason for this: when people were hitting the ball off him, they were hitting it hard. His HR/FB rate was high as well, and he would leave too many meh fastballs over the plate. And so in that case, I wouldn’t want to label his problems merely luck driven…I feel like he has some adjustments to make going into next season.
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by Steve Slowinski on Dec 16, 2010 8:06 PM EST up reply actions
BABIP
When discussing BABIP, I’m not a big fan of jumping right in to talk about pitchers and batters – BABIP is first and foremost a FIELDING statistic.
I’m almost certain DIPS theory does NOT say that all pitchers regress to roughly the same LEAGUE BABIP. DIPS theory says pitchers on the same team regress to the TEAM BABIP the following year? Defense (and parks) do make a difference.
KJOK
Good point about team BABIP
We too often skip that step and incorporate the idea that all defenses are created equal when comparing pitchers on different teams.
by Dan Turkenkopf on Dec 16, 2010 5:56 PM EST up reply actions
Has anyone seen a general MLE for BABIP?
For example: A player that hit for 0.340 BABIP in the minors expects to hit 0.300 +/- 0.040.
I have bee looking at a ton of players and it seems at times a player’s BABIP drops close to 80 points.
- .-. ..- … – / – …. . / .—. .-. - .. . … …
Minor league defense are nototriously worse than major league ones
It seems to me (though I haven’t looked extensively) that BABIP drops significantly in the majors. I feel like this has a greater affect for GB pitchers (who will look worse in the minors than they should), and speedy GB hitters (who look better).
It's not just defenses either
At least in terms of talent, although that is a major part.
Field conditions are much worse in the minors than in the majors too.
by Dan Turkenkopf on Dec 17, 2010 10:00 AM EST up reply actions
Relationship with HRs
Sean Smith’s often hypothesized (or maybe he’s done some basic work?) that BABIP was more of a pitcher skill when HRs weren’t as prevalent. Lots of hard hit balls back then weren’t home runs, but instead in-ballpark hits. Even today, I think we’d get some information by looking at BABIP and HR/FB in concert. If a starters seems to be flukey good in home runs prevented, but has a highish BABIP, they might be related.
Regarding the interaction of BABIP, SO, BB, and HR, my hypothesis is that a pitcher’s talents (velocity, movement, location, interaction of pitches) can produce any combination of those metrics. For example, you could get more SO by throwing more pitches on the edge of the zone and more curve balls, but you’d also likely walk more hitters and give up more home runs on hanging curves. A pitcher needs to find the best combination of those metrics in order to minimize his runs allowed. My guess is that a high BABIP is too harmful and a low BABIP isn’t worth the necessary trade-offs, meaning pitchers with the talent to stick in MLB tweak their approach such that BABIP skill tends to hover around .300.
Yes. This.
I am very much in favor of keeping HR balls in the sample as often as it makes sense to do so.
Also, I agree about a pitcher wanting to wanting to optimize overall results and finding a “compromise” strategy that works for that. Not only is that true as an overall approach, but I think the effect on BABIP, HR/FB, etc., is pushed toward the middle by the distribution of game and opponent situations that a pitcher finds himself in.
He may approach LHB and RHB very differently, power hitters and slap hitters, aggressive hitters and patient hitters, bases empty and runners on, big ballparks with wind blowing in on a cold day and small ballparks with wind blowing out on a hot day very differently, etc., but in the end over a large enough sample he will face close enough to an average distribution of those things that his results will tend toward the middle. This is more true for starting pitchers who go through the lineup a few times than for relievers who may pitch in a particular type of situation with great frequency.
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RH vs LH is interesting.
A pitcher approaching opposite handed batters differently — pitch selection, location, and the flipped direction changes the effect of each pitch dramatically. So it would make sense that the equilibrium established against RH and LH hitters could be drastically different.
I find this thread fascinating. It's in line with what I'd somewhat thought - that BABIP for pitchers is really, really confusing.
Or at least, there are many more variables in play than we tend to assume. If a pitcher has a particularly high BABIP, it may not necessarily be a sign that he’s getting ‘unlucky’, but instead a sign that he needs to make some adjustments if that high BABIP is hurting him.
I love Casey Fossum. Now try and take me seriously.
by Steve Slowinski on Dec 17, 2010 8:32 PM EST up reply actions
This part of the discussion is particularly interesting to me. The idea that pitchers can perhaps control BABIP more than we think, but may benefit more from keeping it closer to average is very intriguing.
I think there is a lot we don’t know about BABIP and some may be using it too often. I know that trying to pass off something as luck or random variation is one of the quickest way to alienate the traditional fan from sabermetrics. If you are going to say that a high or low BABIP is caused by luck, you really need to be able to back it up.
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