Do Catchers Wear Down in September?
It's getting down to crunch time in the final week of the baseball season. While most of the playoff spots are locked up, this week provides some huge games between the Detroit Tigers and Minnesota Twins, both of whom are looking to win the AL Central crown. The Twins have been carried by potential MVP catcher Joe Mauer and they'll likely need him to produce going into tonight's three game series in Detroit.
But for Mauer and catchers everywhere, it's been a long season and the physical strain of the position has to be taking its toll after 150+ games (though because of injury, Mauer himself has only played in 130). They call the catchers' gear the "tools of ignorance" and no small part of that is due to the pain and fatigue which a catcher goes through during the course of a long season. Surely, due to the grind, everyday catchers' cannot be at the same performance level in September as they were in the spring. At least, that's the conventional wisdom. But is it true, and if so, how large is the effect?
Catchers' Drop In Performance
To take a look at this, I studied all catchers who had caught at least 800 games in the retrosheet era. This narrowed the list down to 97 guys who had long careers and played in many Septembers. I then looked at the OPS of these catchers during their careers as a whole and during the months of September and October and measured the difference.
The average catcher in the group had a career OPS of 718 and a September OPS of 707, representing an 11-point drop, which is some evidence that our hypothesis is true. The drop of 11 points of OPS is not huge, but is it significant? The standard deviation of the difference between the career OPS and September OPS was 4.4 points, meaning that indeed there was a statistically significant drop in production from catchers during the month of September (p-value .005). It would appear that yes, the extra wear and tear on catchers does lead to decreased September performance.
But wait. While we do see a drop in September performance, is this unique to catchers? In fact, from the years 1954 to 2008, hitters hit at an OPS that was 11 points less than their full season OPS. So, while we saw an 11-point drop in catchers' performances, we see exactly the same drop in production from all position players. The conclusion is that while hitting sees a drop in September in general, catchers are no more prone to a drop in performance than any other player (a 95% confidence interval for the September catchers effect is between -10 and + 10 points of OPS). The result is somewhat surprising: catchers are able to withstand the grind of a 162-game schedule just as easily as those playing far less demanding positions.
An interesting aside to the question is the way that September offensive performance has gradually been increasing over the past 50 years. The graph below shows the September/full season difference for each year since 1954. As you can see, September OPS was about 20 points lower than the full season OPS in the 50's, but this difference is now close to 'nil. This shift is occurring at about the rate of 0.3 points of OPS per year and a linear model has a p-value of .003, meaning that it is nearly certain that this isn't due to random fluctuation alone. Why this would change is up for debate. One could chalk it up to better conditioning, but of course pitchers are also subject to the rigors of a 162-game schedule and it would seem that they would also improve their conditioning as well, especially considering that teams are far more apt to put their pitchers on pitch counts, presumably helping them stay fresher at the end of the season. I'll let the readers debate this question, but it's an interesting aside to note.