Last time I wrote about Keith Hernandez's excellent book Pure Baseball, which I truly enjoyed. I especially liked the stuff on pitching and the focus of that piece was Keith's take on locating three kinds of pitches: the fastball, the slider and the change-up. Let's start with the change-up—here is what Keith wrote about locating the pitch:
The change-up is never thrown purposefully inside. Never. If the change does what it's designed to do and gets the hitter off stride, about all he can do with the pitch over the outside part of the plate is to hit it weakly toward the end of the bat. But even if he is off stride he can still get the head of the bat on the inside change-up and pull it with power, sometimes with one arm. The pitcher who throws an inside change-up runs a major risk that he will soon be, in the immortal words of George Hendrick, "rubbing up a new one".
This explanation didn't exactly convince me, mostly because I didn't understand it. I believe I understand now, however, thanks to the comments left on Ballhype by sabermetrician Mitchel Lichtman (aka MGL). Basically, Lichtman's point is that the batter needs to swing early on an inside pitch and the swing on a change-up tends to be early anyway, hence the likelihood of "rubbing up a new one."
Ok, so inside change-ups are dangerous pitches and nobody ever throws them purposefully. "Never," as Keith said. "Never" is a big word, so I thought I might have a look at the PITCHf/x data to see if I could learn something about inside change-ups. Keith did say "purposefully," and even the PITCHf/x data, marvelous as it is, cannot tell us where the pitcher was trying to throw the ball. Still we can look at change-up pitch location for some pitchers and see if we can learn something."