Touching BasesMay 13, 2010
Pitching to the Ump
By Jeremy Greenhouse

A couple of days ago, Ben Walker of the Associated Press reported that teams are scouting umpires. I decided to check on the data to see whether pitchers have been changing their approach based on the umpire.

Umpires' zones vary from game to game, yet some umpires develop reputations around the league for perhaps calling the high strike or maybe sleeping next to an ice bucket. For most umpires, the PITCHf/x system has recorded enough data for an analyst to create a strikezone probability distribution. I'm not going to name any specific umpires, since that might come off like I was trying to evaluate them, which I'm really not, but I did make these probability distributions for the league on average as well as for each umpire, controlling solely for batter handedness. I hypothesized that the difference in a pitcher's expected called strike percentage without controlling for the umpire vs. the same pitcher's expected called strike percentage while controlling for the umpire could be attributed to the pitcher's knowledge of the umpire.

I found that, given the internal consistency in the data, there is certainly some skill to this effect, but the magnitude of the effect was small I think. , Livan Hernandez, who you may recall was on the same page as Eric Gregg back in 1997, actually has, by the numbers, done the worst job of adjusting for the umpire, as his pitches were 4% less likely to be called strikes given his distribution of umpires than given an average umpire. While the reliability tests I ran showed that Livan was consistently below average at "pitching to the umpire," I dug deeper, and I can't shake the feeling that luck plays a huge part of it. Sorting through umpires, I couldn't find any difference in Liva's approach. But maybe that's the problem. His approach is consistent, and it's the umpires who change. Here, I present a pair of charts displaying data on Livan Hernandez pitching to an umpire who has called a couple of his games.

I've taken the difference between the average strike zones and a given umpire's strike zone. Blue areas represent spaces where this umpire calls fewer strikes than average, and red areas represent spaces where an umpire is more generous. I made a density estimation to model the distribution of Livan Hernandez's pitches against batters of each handedness, and then plotted a contour line that displays where he's generally pitched over the last few years. I finally plotted the locations of the individual pitches that Livan has thrown with this specific umpire calling the game.


It turns out that against righties, this has been Livan's favorite umpire. The ump does a great job calling pitches below the knees, and he gives pitchers the down-and-away strike, which is right in the center of where Livan generally pitches. So Livan, who has been 7% more likely to have a pitch called a strike with this umpire behind the plate than an average ump, hasn't actually done anything different. This ump just suits his style.

Meanwhile, against lefties, Livan pitches exclusively away, and he hasn't changed up his approach, even though this umpire does not tend to give pitchers that call. So in this way, Livan, without doing anything differently, is failing to "pitch to the ump."

This type of information could also be of value to a manager in deciding whether to throw a sinkerballer who pitches down in the zone or a power pitcher who goes up the ladder. I don't think that pitchers should, or do, change their approach much based on the umpire behind the plate. However, every inch counts, so the information can't hurt.


How do you account for the fact that the hitter can adjust his approach based on the umpire too? Seems like a complicated game theory situation.

M, I didn't use any actual called strike percentages, so I didn't have to control for the batter.

First off, this data is amazing. Second, if teams aren't scouting umpires than I think your findings suggest they should be.

"I don't think that pitchers should, or do, change their approach much based on the umpire behind the plate."

I don't know whether they do or not, but why would you say that they SHOULD NOT? Of course they should. Wouldn't that be more optimal pitching? If an umpire called all pitches from the toes to the knees strikes and all other pitches balls, would you think that a pitcher should alter his pitching style? Of course he should. When someone should do something when you construct a thought experiment using extreme circumstances, is is almost always correct to do that same thing (to a lesser degree of course) in less than extreme circumstances, even in very subtle ones. Of course, if a pitcher CAN'T do that for some reason (e.g., it throws his whole game off), then he shouldn't, but before we declare that a pitcher should not alter his pitching style to conform to certain umpires, we need to know whether in fact it WOULD throw his whole game off. I think that we have to start with the assumption that he CAN alter his game to pitch more optimally against certain umpires. If he can't do that, then why and how would he be able to pitch differently against different batters? Are not the tendencies of the umpires very similar to the tendencies of the batters? If a batter has trouble with sliders in the dirt, then a pitcher will throw more of those. If a batter cannot lay off the high fastball (out of the zone), then the pitcher will throw more of those. If the UMPIRE calls more strikes below the knees than the average umpire, then the pitcher should throw more of those!

MGL, yes, you understand game theory in general and how it applies to pitching strategy very well. Understood.

The point I was trying to make, which I didn't articulate, is that a pitcher might want to throw his slider an inch or two more outside because of the umpire's strikezone, but he shouldn't throw a fastball inside instead of that slider because of the ump's strikezone. So a pitcher should change his intended location a bit, but I don't think he should change his approach. If that makes sense. The difference between umpire's zones aren't large enough or stable enough for a pitcher to move away from his strengths.

The difference between umpire's zones aren't large enough or stable enough for a pitcher to move away from his strengths.

Ditto. Against LHH you can see that the high part of the zone is where umpires are more generous, however, Livan would be nuts to go up there with his 85 MPH fastball.

Jeremy, you did not articulate your position very well at all. Either a pitcher should change his approach when facing different umpires or he should not. The answer is that he SHOULD. You said that he should NOT. If you want to now say that "approach" does not include a slight change in location on some pitches, that is a little bit of a stretch in my book. ;) Who ever said that "approach" means types of pitches but not location? "Approach" means everything.

On top of that, he would probably also change the type of pitches he throws against different umpires, at least a little, since different pitches are more or less effective against different strike zones.

If a certain umpire has a high strike zone, I am sure you will agree that some pitchers at least would benefit from throwing more fastballs (since fast fastballs tend to have more value when thrown up in the zone), and if an umpire had a low zone, some pitchers would benefit from throwing more sinkers or more off-speed pitches.

Again, let's do the "extreme" thought experiment: An umpire only calls strikes from the waist to the letters. What do I throw? I probably throw almost nothing but fastballs. Off-speed pitches are not going to be effective up there. Another umpire only had a knee high strike zone. What do I throw? I can probably throw some fastballs, but batters will not swing at most of them eventually, but they will certainly swing at lots of off-speed pitches at the knees. So again, it would follow that pitchers, in general, should also change their pitch percentages to SOME extent (no matter how little that "extent" might be).

So I am afraid that your "approach" defense doesn't fly either. ;)

After reading all the statistics gathered here. Could someone please explain how todays ballplayers earn the salaries they do. I started watching and listening to baseball in 1947,and since the inception of the closer,setup man and designated hitter, I have watched it deteriorate to the sorry state it is today. If baseball authorities (owners too)did not believe in the mediocre product they were pushing maybe steroids and 100 pitch count games would be unheard of

This is an interesting item. For a decade or so now, I have been advocating for teams to investigate juggling their rotation to favor the umpires. Not completely, but to tweak it to match the HP ump. Wide strike zone? Run Tom Glavine out there. High strike zone? Get a hard thrower in there. Low strike zone, get your sinkerball guy up there.