Tim Lincecum is a starting pitcher for the San Francisco Giants. For the first five years of his career he was one of the best pitchers in the majors, with a cumulative ERA of 2.98. This year, however, he has been atrocious, with an ERA currently at 5.93. I decided to take a look at pitch-by-pitch data to see if I could make anything of it.
I noticed that he had an unusually large difference between home and away ERA--3.43 at home, but 9.00 on the road. Coupled with the source of home field advantage, I decided to investigate something: could his difference in play this year come from umpires restricting his strike zone?
As it turns out, no. In both 2011 and 2012 about 10% of his pitches that batters didn't swing at were balls miss-classified as strikes by the umpires, and about 2.5% were strikes that were called balls; umpires were no harsher this year than last.
I then took a look at placement. In particular, all else equal better pitches are generally around the edge of the strikezone, and worse pitches are generally either right down the middle or way outside the strikezone. So, I decided to look at the average distance from his pitches to the vertical and horizontal edges of the strikezone; this time there was a difference. In 2011 the sum of the vertical and horizontal misses from the edges of the strikezone averaged .923 feet; in 2012 it averaged .961 feet. It doesn't seem like a huge difference, but it is statistically significant, with just a 2% chance of occurring randomly (having a t-test value of -3.23). So, it does seem like his control is down from last year.
I also looked at the velocity of his pitches. There's been a lot of talk about his velocity decline; the decline, as it turns out, is real but not that precipitous: his fastballs and sliders have slowed down by about a mile per hour on average, though his changeup and curveball are still at roughly the same speeds there were in 2011.
So Lincecum's pitches are slower and less controlled than last year; in the end it just looks like Lincecum is pitching worse this season.
Is there anything else I should look at?