The foul ball, part one: What does it tell us about a batter?

No one likes foul balls.  They don’t accomplish anything, and the two strike variety in particular actually does nothing at all to move the game along.  In fact, it used to be that the foul ball was a non-pitch, no matter how many strikes were on the batter.   Really, the only good that a foul ball does is give some kid a souvenir that he’ll treasure forever.  (Admit it, if you’ve caught one or even gotten close to one, you can tell me the date, opponent, score, who hit it.  Even if you’re 40, it was a meaningless game, and Steve Lombardozzi hit it.)
But what of the foul ball?  Everyone hits them.  Some hit more than others.  But can they actually tell us anything about a batter?  Surprisingly, yes.  So, as we begin our look into the foul ball, let’s create a few metrics.  First off, Retrosheet has data on the fact that a foul ball was hit, although doesn’t tell us exactly how foul the ball was.  For example, was it just poked to the first base coach, tipped at the plate, or a monster shot down the left field line that just… hooked… foul?  That limitation aside, we can still create some simple metrics.

• Foul balls per plate appearance
• Percentage of total pitches fouled off
• Percentage of pitches with which the hitter made contact that went foul (foul contact)
• Overall swing percentage and overall contact rate

Additionally, there are two “types” of foul balls.  There are the foul balls committed when there are 0 or 1 strikes (which count as a strike) and those that come with 2 strikes (which don’t).  We know that with two strikes, a batter will often go into “protect” mode and swing at borderline pitches, figuring that if he swings and fouls them off, it’s not the end of the world.  So, we will split these two types of foul balls apart, and create two metrics.  One is for 0-1 strike foul balls per plate appearance.  The other is for 2 strike foul balls per plate appearance in which the batter actually had two strikes on him.
First off, let’s see if fouling pitches off is a repeatable skill.  For example, we know that some players are pretty consistent home run hitters, but are there foul ball hitters?  I subjected all of the above new metrics to an intra-class correlation (a measure of how consistent players are across years… think of it as a year-to-year correlation but with the ability to incorporate multiple years of data), using four years worth of Retrosheet data (2004-2007).  Results were pretty encouraging.  With a minimum of 250 total PA for the season in question, foul balls per PA checked in with the lowest intra-class correlation of .574.  All of the other stats reached into the mid- .60 range or better.
Now, while that’s nice to know that players are generally consistent in how often they generate foul balls, do those foul balls actually tell us anything useful.  I looked at a bunch of batting statistics for some answers.  I looked at usual “slash” stats (AVG/OBP/SLG), along with the batter’s batted ball profile, walk rate, strikeout rate, single rate, double-and-triple rate, and HR rate.  I ran a gigantic correlation matrix to see what turned up.  The first thing to note is that just about everything was statistically significantly correlated with one another.  I took all players from 2000-2007 with a minimum of 250 PA and ended up with a sample of 2400+ player-seasons.  At that kind of sample size, it’s all significant, so our analysis will deal more in the strength of the correlation.
What’s interesting is that 0 and 1 strike foul balls per PA had a correlation with two strike foul balls in two strike PA’s of .106, which is rather low.  This says that they are two relatively independent “skills.”  Knowing about a player’s general foul ball count isn’t enough.  You have to differentiate between the two.  There’s other evidence that we are dealing with two different skills with two different types of etiology.  Hiding in the correlations between the swinging metrics that I created, there was an interesting pattern to be found.  Foul contact percentage  was correlated with 0 and 1 strike foul ball rate at .487.  The correlation with two strike fouls was a mere .150.  Looks like 0 and 1 strike foul balls are more the result of a player who can’t straighten out his swing.  Then, there’s the issue of overall contact percentage.  The correlation between that and two strike fouls is .524 while the correlation with 0 and 1 strike foul balls is -.366 (note that’s a negative).  So, a player who makes a lot of contact is likely to have a lot of two strike pitches that he spoils, but fewer foul balls for strike one and strike two.
Do foul balls correlate with any of the actual outcome stats?  Well, the usual slash stats didn’t correlate well with any of these new metrics.  But, some specific outcomes show some rather intriguing patterns.  A batter who hits a lot of two-strike foul balls is less likely to strike out (r = -.482) and less likely to walk (r = -.345).  Makes sense, since he is more likely to extend his at-bats until (assuming he actually doesn’t end up walking or striking out) he puts the ball in play.  And put the ball in play he usually does.  Two strike foul balls are moderately associated with an upswing in singles rate (r = .347), but a downturn in HR rate (r = -.215) and HR/FB (r = -.300).  This pattern becomes even more pronounced when one looks at overall contact percentage (which we’ve already seen is a pretty good correlate of two-strike foul ball hitting).  The correlation with strike outs hits -.875, which makes sense because you can’t strike out if you hit the ball, foul tip into the catcher’s glove notwithstanding.  Overall contact is correlated with more singles (r = .549) and fewer HR (r = -.521).
What about zero and one strike foul balls?  The correlations with the outcome measures aren’t very strong.  However, foul contact percentage predicts the opposite pattern of overall contact.  Strikeouts go up (r = .669), singles go down (r = -.454), and homeruns go up (r = .410).
What’s funny is that if you just look at foul balls per PA, the correlations are not really that interesting.  Most of them are below .20, which isn’t much of anything.  A lot of the effects seem to wash out when you look at all foul balls together.  You really have to break them down into their component parts before you can fully understand what’s going on.  Foul balls early in the count speak of a player who doesn’t make a lot contact, when he does make contact he’s not likely to hit it fair, who strikes out a lot, but when he hits the ball, it’s more likely to go out of the ballpark.  There was one other thing that jumped out.  Foul contact percentage was (moderately) correlated with a lower ground ball percentage (r = -.318) and a higher fly ball percentage (r = .297).  So, we have guys who appear to be trying for fly balls, and fly balls that will leave the park at that.  That’s a higher risk swing, and more likely to go awry, either by swinging and missing or swinging and having the ball go foul.  Two strike foul balls speak of a hitter who makes good contact, keeps at bats alive, but is generally just a singles hitter.  Low risk, low reward.
So if you want know what’s going on with your favorite player, the one who seems to be acting a little weird lately and all you have is a box score, take a look at his foul balls.  They might provide you with a useful little diagnostic of whether he’s feeling a little risky or if he’s playing it safe lately.  I suppose there could be the case where a hitter is high on both types of foul balls (or low on both), and the effects would seem to cancel each other out.  (Remember, total fouls per PA aren’t really correlated well with anything.)  But, if you see a lot of one type and not a lot of another, you can perhaps come to some conclusions about what’s going on in the batter’s head.

8 Responses to The foul ball, part one: What does it tell us about a batter?

1. studes says:

Nice job, cutter. How about some of the data to go along with the correlations? Player examples, with their stats?

2. joe arthur says:

“Foul contact percentage was (moderately) correlated with a lower ground ball percentage (r = -.318) and a higher fly ball percentage (r = .297).”
Foul ‘fly’ balls have a possibility of being caught and terminating the at-bat. Are you recognizing these ‘balls in play’ as foul balls? With foul balls a little more common on swings with a two strike count, ground ball foulers will be a little more likely to keep getting chances to swing with two strikes. What correlation would you get if you limited to 0 and 1 strik e counts?
I don’t like the terminology of “foul ball skill.” If there is such a skill, batters should only be deploying it when defending the plate. In general, batters’ skill is to hit hard fair balls. Foul balls are a byproduct of that effort, when a hitter “misses” slightly: high or low, and/or early or late. Pull hitters should have a bias toward missing ‘early’ more often than ‘straightaway’ hitters, so they should have more squarely hit balls landing foul rather than fair. It may be pull hitting rather than power hitting per se which causes the correlations you observe.

3. Mike Fast says:

Pizza, I’m curious if pitchers show foul ball skills. From my look at PITCHf/x data, I would certainly believe the answer is yes, but I’m even more curious if they also have two distinct skills at 0/1 strike and 2 strikes. That’s not something I’ve looked at separately, but it would make sense.
Brian Bannister had an awful lot of two-strike fouls last year, implying that he didn’t have a strikeout pitch.
Then it would be interesting to see what happens in the confrontation between hitters who are able to defend the plate with lots of two-strike fouls and pitchers who are able to put the batter away with few two-strike fouls, as well as the other combinations of matchups.

4. Pizza Cutter says:

Joe, good point on foul flies. Hadn’t adjusted for that. I’m not a fan of “foul ball skill” either, because it makes it sound like something we should encourage. I suppose the more proper term is “repeatable performance.” But that just doesn’t sound right.
Mike, you’ve anticipated Part 2. I haven’t run the analyses yet, but that’s the topic.

5. Pizza, what stands out the most to me here is the outcome/lack of outcome on certain stats. For instance, I watched Bobby Abreu intently for 8 years here in Philadelphia and he is just a tremendously smart hitter; knows the strike zone, seemed to show a persistent ability to spoil pitches, etc, but it always seemed like his best at bats, in terms of linear weight outcomes, involved ones wherein he saw fewer pitches. When he saw more pitches he tended to walk or line a single to right field. When it was a 2-0 count he would double or homer. I’m not sure if the stats back that up and if I am influenced by watching him all of these years but I think that’s incredibly interesting.

6. Pizza Cutter says:

It makes sense in terms of mindset. When you have a 2-0 count, you can take more of a chance with your swing. When you try to swing hard, you have to pick one area in which you will concentrate the swing, and it doesn’t leave a lot of room to change midway. If you guess right, you get a very hard hit ball that’s more likely to hit the wall or go over it. If not, you swing and miss. On a 2-0 count, you come back and try to get him on 2-1. With two strikes, you have to take a shorter, softer swing with more room for plate coverage. If you take a big swing and miss… well, it’s 1-2-3 strikes your out at the old ball game!

7. Change the rules (it’s allowed):
1. Start the count at 3-2.
2. Only fair flies caught are outs.
Put the damn ball in play, that’s the entire point. The pitcher should facilitate that, not hinder it.