Based on his breakout 2011 season, we knew Justin Masterson was capable of the impressive performance he’s put forth thus far in 2013. But how he’s reached this point is somewhat surprising.

We know Masterson as a sinkerballer. There have been games in which he’s thrown the pitch over 95 percent of the time, and in 2012 he threw 79 percent sinkers overall (no other full-time starter reached more than 56 percent).

But Masterson has always worked in an occasional slider to keep hitters on their toes, and this season Masterson seems more confident in his slider than ever.

Through three starts, roughly one out of every four pitches has been a slider, and opposing hitters are a combined 0-22 in plate appearances that end with the pitch.

So why is it working?masterson slider

It’s still very early in the season – he’s only thrown 82 sliders overall – but so far the pitch seems to be fooling hitters more than ever.

Of the 82 sliders Masterson has thrown, hitters took 49 of them (60 percent). And of those 49 takes, an incredible 24 were called strikes (49 percent).

Over the previous three seasons, Masterson’s called-strike rate on sliders were 30.9, 30.5 and 30.0.

Obviously this is a dramatic deviation from the norm for Masterson, so a slight regression back to the established trend is likely. But it’s also unlikely that’ll completely regress to his form from the previous few seasons.

The fact that Masterson has increased his slider workload and seen dramatically improved results isn’t a fluke. According to The Plain Dealer, he worked extensively on the pitch this offseason in an effort to lighten the load on his arm from throwing so many hard sinkers.

So far, the results have been even better than expected.

Non-Fastballs with the highest percentage of called strikes this season (min. 75 pitches):
Bronson Arroyo’s curveball – 53.1 percent
Justin Masterson’s slider – 49.0 percent
Tommy Hanson’s slider 47.9 percent

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