Indians right-hander Justin Masterson on Monday afternoon thoroughly laid waste to the Yankees in the course of a 1-0 victory: 9 IP, 4 H, 0 R, 9 K, 3 BB. Of those four hits, none went for extra bases, and three were of the infield-single variety. Perhaps most impressive is that Yankees manager Joe Girardi stacked his lineup with six left-handed batters, but Masterson was able to thrive despite all those opposite-side challenges. And therein lies the story of Justin Masterson in 2013.
Monday's sparkling gem -- look at it sparkle! -- lowered Masterson's ERA this season to a nifty 3.14 and his FIP (go here for an explanation of what FIP is) to 3.09. Compare those numbers to what Masterson wrought in 2012: a 4.93 ERA and 4.16 FIP in 206 1/3 innings of work.
In large part, he has improved because his performance against left-handed hitters has improved -- kind of.
Consider that, from 2008 through 2012, left-handed batters hit .292/.367/.432 against Masterson, which is far from optimal, particularly in the on-base department. In 2013, however, Masterson has allowed a slash line of .256/.350/.355 to the opposite side. The OBP is still too high, but at least he has driven down the power numbers.
In part, the difference might be attributable to pitch selection. Courtesy of the essential Brooks Baseball, here's how Masterson has worked the opposite side over the entire span of his career, including 2013:
And here's how Masterson has pitched left-handed hitters in 2013 alone:
As you can see, Masterson against lefties is leaning much more heavily on his slider, at the expense of his sinker. That would seem to be a curious decision, since right-handed sliders tend to break in on left-handed batters and as such generally show notable platoon splits, as individual pitches go.
As for Masterson's slider, it does indeed break in on lefties. But since last season, he has significantly increased the horizontal movement on the pitch (source: FanGraphs). As such, perhaps the pitch has gone from the wheelhouse of left-handed batters to the kitchen of same. Indeed, the opposite side this season is batting .177 and slugging .268 against Masterson's slide-piece this season -- paltry figures, both (per Brooks). The fact that Masterson goes to the slider 38 percent of the time on two-strike counts suggests that he's starting to wield it as an out pitch in platoon-disadvantaged situations.
That's the good news. The not-as-good news is that some of Masterson's deeper indicators suggest that his success against left-handers isn't all that it seems. Joe Sheehan recently wrote about the importance of looking beyond slash lines when evaluating platoon splits, and indeed Masterson's performance against lefties isn't as impressive under those conditions.
For instance, Masterson in 2013, according to FanGraphs, is striking out just 17.1 percent of left-handed batters while walking 10.7 percent of left-handed batters. In 2012, when he struggled against lefties in terms of runs on the board (they raked to the tune of .296/.376/.450 against him), those figures were similar: 13.5 K%, 10.5 BB%. Sure, he's missing bats at a slightly higher rate this season, but that's not a substantial difference in terms of his ratio.
That Masterson seems to have harnessed that extra movement on his slider is a good thing, and there's certainly reason to believe he has improved against the opposite side on an overall basis. Until those command indicators (i.e., K% and BB%) improve, though, let's temper the enthusiasm just a bit.
So Masterson is indeed showing signs of reaching the next level, but he hasn't reached that next level just yet.
Note that I said "yet."