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Friday, December 09, 2011
Velocity as a scouting variable
Matt follows up John Mayne’s article from almost two years ago, with his article.
I’m not really surprised by the results. However, I’d like to correct Matt’s interpretation when he says things like:
Not only do pitchers who throw faster succeed more often, but they improve more as well.
Let’s go back to what ERA and component ERA (like FIP) tells us: it is an INFERENCE of their true skill, based on the OBSERVATIONS available. That’s all these things are. If all I know is his K/PA, then I can infer how good he is, with a certain confidence interval. If I know his BB and HR and BABIP, then I can infer better.
So, if you have two guys who have an identical K, BB, HR, BABIP rates, but one also happens to throw 95mph and the other throws 90mph, then we can INFER that the harder thrower guy has less good luck in his ERA than the 90mph guy. It’s more real for the harder-thrower than the softer-thrower.
The job of the saberist is simply to figure out: how much more real. That’s the only job of the saberist, to infer as best he can, given the observations at hand.
Now, if the softer-thrower actually locates his pitches better, then that’s another variable to consider.
But, the important point is this: ERA is simply an observation, and observation that has a certain amount of good luck and bad luck.
It’s more obvious with things like steals per SB attempt. If one guy can run from 1B to 3B in 6.2 seconds, and another guy can run that in 8.2 seconds, and both guys have an 80% SB success rate, guess which guy got luckier? Now, obviously, you want to measure things like jump and reading-the-pitcher, etc. But, given a large enough group of players, say 20 in each, those kinds of things will likely cancel out. So, you’d bet on the faster guys to have a better success rate (since this will presume “all other things equal").
And, hard-throwers are more likely to perform better than soft-throwers, all other things equal.
Fair point. I should say, “Not only do pitchers who throw faster succeed more, but their ERAs improve more; and not only do their ERAs improve more, their peripherals improve more as well!”
In other words, it’s not just that the pitcher with bad velo and a good ERA had some good luck. It’s that even if he was striking guys out, he had some good luck. It’s even informative about luck in peripherals and stats that stabilize quickly!