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I’d like to see the r=.50 analysis done on fastball speeds. Jeff notes:
As a general rule, one game of fastball speeds gives some useful information, but after 3 games a pitcher is generally throwing within 1 MPH of what they will average the rest of the season.
I was going to state the same thing. It is really quick, especially if you adjust for park differences (like Mike does for most of his work).
I was playing around with some numbers (just pure guess numbers), as I though Mike’s number was probably an exagerration. As it turns out, it’s not that far off!
n=2 is my best guess, though n=1 is a pretty darn good guess too.
So, if you see someone with 10 fastballs averaging 95, and the league average is 90, then with k=1, you regress that 95 1/11th to 90, or about 94.5. At k=2, you regress 95 2/12ths to 90, or about 94.2.
I was actually planning on looking at this (along with some other PITCHf/x-related stats) in the near future. I too would have guessed fastball velocity stabilizes incredibly quickly, as it seems it does.
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My guess is that r=.50 by somewhere around one fastball. It stabilizes incredibly quickly.