Baseball defense is hard to measure. Catcher defense is even harder. There are a lot of different aspects of catcher defense, including:
- Controlling the running game
- Actually fielding the ball
- Preventing passed balls and wild pitches
- Pitch framing and umpire psychology
- Game-calling and pitcher psychology
For the longest time, #1 was all we looked in stats like WAR. #2 a comparatively small part of the game while also being difficult to measure. #5 is anyone’s guess. Some work has been on #3, but I’m not sold on it yet. That leaves us with #4: getting umpires to call balls as strikes, and strikes as strikes.
Measuring pitch framing is actually pretty easy. We have Pitch/Fx data about where a ball ended up. We have a good idea of where the strike zone should be. Therefore, we can count up pretty large sample sizes of called strikes that should be balls, and called balls that should be strikes. Do the math, and you know how many more strikes a catcher was able to call versus the average.…