Monday, December 21, 2009
What differences can we discern between a pitcher’s best and worst starts?
Not a whole lot, at least for A.J. Burnett, according to this excellent article by Nick Steiner.
About “stuff,” he says:
So I think we can say, for all intents and purposes, that there was no practical difference in the quality of Burnett’s stuff in his best and worst starts of season. That’s not too surprising as stuff is primarily a matter of mechanics. Location, on the other hand, also includes release timing and intent, two things that you would expect to add a lot more variance from start to start.
That may not be too surprising to him, but to any traditional baseball person, I think that would shock them. If you pitch badly, your stuff is generally no good that day, right? Why else would you take your ace out in the 4th inning when he has given up 6 runs (in 80 pitches)?
His conclusion:
So what did we learn today with this obnoxiously long article? Well I took a pitcher’s 10 best and worst starts of the year, in which you’ll remember there was an ERA difference of about 8, and found no meaningful differences in terms of what he threw, the velocity/movement of his pitches, where he threw them and when he threw them. I think I’ve established that there was practically no difference in how he pitched in his good starts compared to his bad starts.
Does this show that all peaks and valleys of performance over a long season are simply due to luck? Of course not. Burnett is only one pitcher. However, I believe that this is a strong piece of evidence to support that notion to some extent. I hope someone smarter than me will develop a way to quantify the expected production of a pitcher using PITCHf/x data. Then we could apply it to the population to see if the phenomenon I found today holds true for most pitchers.
Thanks for the link MGL, I’m glad you enjoyed the article. The “too surprising” part was just me intentionally understating my case. The location section was the real kicker, and I wanted to build up to that.
Anyway, I was surprised just how little of a difference I found. I suppose there could be something going on with deception, or he could have been pitching more to batters weakness in the good starts (that wouldn’t necessarily show up in aggregate location), but in the absence of that, there was practically nothing separating the two groups of starts.
If anyone else want’s to look at the data, here you go.
Good starts
http://spreadsheets.google.com/ccc?key=0AmhtqthzQ8zFdDFnejM3QTRYS0Rkbkp0WHFtVVUyUXc&hl=en
Bad starts
http://spreadsheets.google.com/ccc?key=0AmhtqthzQ8zFdHFtU1lBam1BQ01YNlhuZ2xwc3gyQmc&hl=en