Pitch f/x for Dummies

Since nobody cares about anything I post that isn’t raw, hard, data, I should probably explain once and for all what these charts I pump out really mean and then just link to this post for newcomers to the pitch f/x world. I used to gush on and on about system, but these days can’t even bring myself to mention that they’re from the catcher’s perspective before launching into a dizzying sequence…

First, what is to me the most interesting and useful data- pitch movement. Using my favorite graph from a splendid Shaun Marcum outing, here’s the complete catalog of pitches (except the splitter which is almost indistinguishable from a changeup but thrown harder) and what they look like:

As you can tell from superimposed Marcum, we’re looking at the pitch from the hitter’s perspective from whichever side he throws from. A 4-seam fastball is as “straight” a pitch as there is, and then breaking balls go one way and sinkers and changeups tail the other. The scale is in inches.

This does understate the knee-buckling quality of a curve or any other offspeed stuff, because they go up and then come back down more than a hard cutting pitch but don’t necessarily end up anywhere different than a hard cutting pitch. Pitch f/x does also measures this “break”, I just never use it because I like movement as a quick way of seeing what is working for a pitcher on a given night. Contrary to popular belief, there are no “late breaking” pitches- once the ball leaves the pitchers hand, it acccelerates at a constant rate. Anything else is an optical illusion (like a “rising fastball).

Now for pitch location:

Pretty self-explanatory…The average strike zone in the majors is from 1.6 feet at the knees to 3.5 at the letters. Pitch f/x records the top and bottom of the strike zone for every batter, and I adjust every pitch based on it. So if a pitch catches the top inside corner of the zone for a monster like Frank Thomas, it will appear in the same place as that for David Eckstein.

The sides of the plate are a little tricky. First (and the graphic you see on TV doesn’t seem to be aware of this) you have to add an inch and a half to the zone because the system measures the dead center of the ball, and if any part of it goes over the plate then it’s a strike. Second, major league umpires on average give another 2 inches or so (more for lefties, less for righties) off the edge of the plate, and don’t give calls on the corners as much as they do pitches at the belt. But the yellow outline is the technical strike zone.