I recently wondered aloud, in one of my league’s chat rooms, why Cleveland Indians pitcher Justin Masterson is having a renaissance season, noting his wildly improved strikeout rate. Another owner (who is conveniently a Red Sox fan and therefore semi-invested in knowing how Masterson does for the rest of his career) told me as long as Masterson is still a sinker-ball pitcher, he will revert back to his old ways. I assumed he would be right. The strikeouts really came out of nowhere. And I mean, shoot, I didn’t even know Masterson was a sinker ball pitcher before my friend mentioned it.
Still, I decided to look into the matter to see what’s really going on. The following, thanks to FanGraphs’ compilation of PITCHf/x data, revealed the following: Masterson has saved the most runs of any pitcher this year using his slider. (His slider has saved the third-most runs proportionate to his total pitches thrown, behind the very legit Jose Fernandez and very fat Bartolo Colon.)
Which made me wonder further: Has he always been this good with his slider? Has he always thrown it this often? Besides, the PITCHf/x technology is relatively new (installed in 2006), and FanGraphs admits it may occasionally mistake pitches thrown by a pitcher. For example, Masterson’s sinker could perhaps be mistaken for a slider.
The answer to the questions I posed, however, is a resounding no. He has thrown his slider this year 8.4 percent more often than last year at an average of 8.5 mph slower than his sinker ball, so there should be no mistakes made there. On top of this, he is recording career bests in not only swinging strikes but also swings and misses outside the strike zone.
Ipso facto, his slider has been filthy this year. And the swinging strikes and out-of-the-zone whiffs attest to his 9.18 K/9, good for 14th of all qualified starters.
FanGraphs specifically warns of the descriptive, and not predictive, nature of PITCHf/x data. Deviations from a certain benchmark for PITCHf/x data do not necessarily indicate bad luck, good luck, pending regression or anything like that. However, the descriptive nature of the metrics on Masterson’s slider indicate he can (probably) attribute his bounce-back year to his slider. And if you’re looking for something predictive, I predict if Masterson continues to use his slider and hone his sinker, he will continue to be effective.