Catching might be the most exhausting job on the field. While everyone else can stand up straight and meander about their appointed pasture, you, the pitiable catcher, have to crouch behind the plate. And stop 90 mph balls with your glove. And call the pitches. And be the front-line psychologist for the pitcher. And take foul tips off the chest protector. And… oh dear, R.A. Dickey is pitching today. Plus, you gotta hit and run and sign autographs for the 8-year-olds.

It’s no wonder that teams employ two catchers and even if one is better, he gets regular days off. Otherwise, as the story goes, he might break down from all the mental exhaustion. Call it the Salvador Perez Effect, after the patron saint of overworked catchers. There’s a short list of “Thou shalt nots…” with catchers. They’re not allowed to catch both ends of a doubleheader. They shouldn’t catch a day game after a night game. It’s nice to have the backup catcher be paired up with one of the starting pitchers as his “personal” catcher, so that the starter gets a scheduled day off on a consistent basis.

But here’s a question. Why? Yes, it’s generally accepted as a practice that teams should be a little more ginger with their catchers, but does it actually make a difference?

Warning! Gory Mathematical Details Ahead!

All data are from 2011-2015. I first created a database of catcher appearances, sorted by calendar date, and for each game that a catcher appeared in I coded whether he had also caught the day before (not necessarily the game before, because of off-days in the calendar) as well as two days before, three days before, and so forth.

I tried several different strategies for trying to pick apart who the well-rested catchers were vs. the overstressed ones, but settled on three pretty good ones. Did he start yesterday (vs. nope)? How many starts has he made in the past seven calendar days? Is he a guy who got the day off yesterday or is he a guy who is starting on his fifth straight calendar day? On that last one, if we’re going to find a catchers when they are running on fumes vs. when they are well-rested, that ought to do it. (Careful readers will note that I am looking at catchers who are starting. When I took that restriction off, it all said the same thing. Actually, it didn’t matter how I did it. They all said the same thing.)

I also limited the sample to catchers who caught at least 100 games in the season in question. The reason for that is “hasn’t started in three days” is probably a pretty good proxy for “backup catcher” which might be a proxy for “not a very good catcher” but at the very least is a good proxy for “has lived on a much more lenient rest schedule.”

First, I looked at whether a “tired” catcher behind the plate led to the batter in front of him having an easier time. Maybe a tired catcher isn’t calling a good game or maybe he’s a little less sharp in framing things up and a few would-have-been strikeouts go slip sliding away. Then again, we also know that the catcher—compared to the contributions of the pitcher and batter themselves—actually has relatively small part to play in all of this.

I used the log-odds ratio method to control for pitcher and batter quality and looked to see, within a regression, whether any of our measures of catcher tiredness had any effect on what happened in front of the catcher, beyond our expectations based on just their seasonal stats. I looked at a bunch of different outcomes (strikeouts, walks, singles, outs on balls in play, grounders, flyballs, home runs…) Not one of them was affected by the fatigue status of the catcher, no matter how I defined “fatigue.”

Okay, fine. Maybe catchers who have been donning the tools of ignorance day after day after day are worse at doing catchy stuff. I isolated all instances where a team had a runner on first with second base open, and controlled for the general tendencies of the pitcher and catcher to allow stolen base attempts and stolen bases in general. Perhaps teams were more likely to run on “tired” catchers? I saw no evidence that teams altered their running games to be more (or less) aggressive. Considering that there’s no evidence that catchers were any less effective at throwing out would-be basestealers, that’s probably not a good or a bad thing.

Well, what about blocking balls? Again, I controlled for the likelihood that the pitcher on the mound would throw a wild pitch or would throw a wild pitch that the official scorer would say was a passed ball and the catcher’s general tendencies to allow such things to happen. (Obviously, only in plate appearances featuring a runner on base.) Were tired catchers worse at preventing balls to the backstop. Nope. Even when I looked only at passed balls (which is the official scorer’s way of saying that it was the catcher’s fault) there was no effect.

So, it seems that the catcher isn’t doing anything differently behind the plate when he’s been going for a couple of days in a row. At least the results are the same. What about when he comes to bat?

Again, we’re looking at catchers who caught at least 100 games, so these are regulars. The only thing different is that on some days, they’ve rested and on some days, they’ve been going for a while. I controlled for the catcher’s general offensive proclivities and those of the pitcher whom he is facing. Are tired catchers more likely to make outs or less likely to get hits or more likely to strike out—compared to their own baseline rates—when they’ve had a heavier workload?

Nope. This was a total shutout. I didn’t even have a stray significant finding to say “Meh, just building Type I error.” A lack of rest doesn’t seem to hurt (or help) catchers in any way. They just keep plugging along.

Okay, well, maybe it’s the stress of a long season that gets to the catcher. I’ve previously written about “The Grind,” the observable phenomenon by which players tend to do a tiny bit worse at making good decisions in the strike zone as the season wears on. It’s not a huge effect in practice, but tiny, consistent effects can compound over the course of a season.

I ran an analysis to see whether The Grind affects catchers moreso than it affects non-catchers. It turns out that the effect is somewhat less for catchers. As the season rolls along (denominated in calendar days since Opening Day), there’s a downward slope in plate discipline for everyone, but catchers get off a little easier. It might be that the fact that catchers get so many off days keeps them a little fresher.

Walking It Back
Before someone takes this an endorsement to just have poor Salvy catch ALL OF THE GAMES, let me walk this back a little bit. There’s probably an upper limit to how much abuse a catcher can take. This is a good example of needing to understand the ecosystem in which your training data set was collected. Maybe the reason that a catcher catching on his fifth day in a row doesn’t seem to have many ill effects is that he really only does this once in a while. And on top of that, he generally gets a lot of breaks. Plus, the reason that he’s out there is that someone (his manager) did an evaluation and decided that it was a good idea to send him out there for his fifth straight day. It’s possible that the manager is an idiot, but… actually you don’t get to be a major-league manager if you’re an idiot.

In other words, when interpreting any baseball data, always remember that there are a bunch of very smart people who are being paid to introduce bias into our samples. It’s always good to stop and think about how that should affect our conclusions. I have this tattooed on my left arm.

Let me frame the conclusions from this research within a somewhat imprecise analogy to my own life. As the parent of three small children, I’ve had the occasional sleepless night. The next day, I feel it a little bit, but I am still a functioning adult because I do have a bit of a reserve bank of sleep to fall back on. But rewind to a few years ago when—during one particularly awful stretch—my oldest daughter (when she wasn’t yet a year old) spent most of four nights awake. After the fourth night, my brain was a gelatinous pile of… thing… that was not good… at doing the… brain stuff. Same sleepless night, but in a different context, it had a different effect on me. Had my manager seen me that morning, he wouldn’t have sent me in to catch that day. (Unfortunately, there aren’t days off in parenting.)

If the catcher has had four straight days of catching, but still feels pretty good and hasn’t taken any tough foul balls off his chest protector, and he’s a good catcher, his manager will probably send him back out there for a fifth day. And he’ll be okay… again, assuming that this is all in the normal bounds of catcher usage. If he’s not doing so well, his manager will tell the backup to get his gear ready and tell the starter to take a break, unless the backup is just not available. The manager knows whether the past few days have been easy on the catcher or tough ones and can make his decisions accordingly. If we have any belief that the manager has a clue of what he’s doing, we have to acknowledge right there that he’s bringing bias into our data. (As always, my pleas to MLB to assign playing time to players randomly seem to get nowhere.)

Maybe if a catcher had been behind the plate 20 days in a row, he’d fall apart. Okay, it’s very likely that if he was behind the plate for three weeks straight he would fall apart. The thing is that we don’t have much of a sample size on guys who were actually used like that, and what sample size we do have is highly selected. But if you see a guy who’s being used multiple days in a row, there’s actually no reason to believe that he’s a risk to see his performance suffer, based on that fact alone. Yes, catching is a tough job, but it’s also the job that the catcher has trained to do, so we shouldn’t be surprised when he goes out and does it. The fact that he’s out there means that someone thought he could do it, and maybe they’re right.

Thank you for reading

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Interesting study and lack of result. *Had* you found a noticeable effect, it might have been interesting to control for the disproportionate number of ex-catchers as managers.

As far as the slight "anti-grind" effect, maybe it's the extra rest, and maybe it's that the catcher is a little more engaged, and in a different way, each day with the game situation than the other positions. Less of a SSDD situation, and more of a new puzzle each day.