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Examining the Mets Rotation With xK%

Chin Gee.
Chin Gee.

Maybe Johan Santana is a known known, but there are reasons to wonder about the rest of the Mets' rotation. R.A. Dickey is in the midst of a strikeout-rate surge in a now-relevant sample, Jon Niese has found a new peripheral to dog his solid overall line, and then there's the Rest of the Guys. Not quite "Johan and Dickey and the rest are iffy," but close.

FanGraphs colleague Michael Barr developed an expected strikeout percentage for FanGraphs+ (sorry, pay link) before the season, and though it might not be kind to Dickey, let's run the equation on the Mets rotation and see what happens.

Here's the equation:

xK% = -.278 + (.003)*FBv + (1.428)*SwStr% + (.321)*K% 2010

And now the Mets pitchers, with data courtesy

FBv SwStr% K% xK% FB%
Mike Pelfrey 93.5 8.90% 15.30% 17.87% 62.60%
Johan Santana 88.4 11.70% 25.10% 23.48% 60.10%
R.A. Dickey 83.2 10.80% 23.60% 20.16% 14.90%
Miguel Batista 91.6 6.30% 12.50% 12.69% 55.90%
Jonathon Niese 90.6 8.60% 21.60% 18.59% 48.70%
Dillon Gee 90 10.40% 20.90% 20.76% 50.50%
Jeremy Hefner 88.9 7.90% 15.90% 15.26% 54.60%
Chris Schwinden 88.9 4.80% 2.40% 6.49% 62.10%

Oh Big Pelf, you might have been headed for something... maybe. Johan Santana is beating expectations based on his fastball velocity, but what else is new. Miguel Batista is only supposed to eat innings and write prose, so that's fine. R.A. Dickey's swinging strike and strikeout rate surge has passed some sample size hurdles, but this analysis doesn't fully believe in it. That's why the last column was added -- he's not a traditional pitcher, and his stuff doesn't depend much upon his fastball velocity. Still, even a 20% strikeout rate would be a great leap forward for him, and maybe a recent low in fastball usage is a big part of his newfound whiffiness.

Niese deserves more attention than we'll provide here, especially since he's continued to put up mediocre overall numbers, but has found a new way to do it. Instead of suffering at the hands of BABIP, he's now being tortured by HR/FB%. While he used to have an okay strikeout rate and an above-average walk rate, he now has a strong strikeout rate and a bad walk rate. Through it all, his non-FIP ERA estimators remain in the mid-to-high threes, while his ERA sits in the mid fours. Now this expected strikeout rate says we should expect more of his career rate going forward, meaning it's probably not a good idea to focus just on those extra home runs he's been plagued with this year. What a strange history his peripherals have had, all while his ERA has told a more boring story.

The back of the rotation? More mixed news.

Dillon Gee is striking out about as many people as might be expected, yes, but that fact itself is unexpected. Sporting an unimpressive 90 MPH fastball, Gee's always been about his changeup. But you can't throw your one pitch all the time unless you are Mariano Rivera, so he's mixed his stuff around and used an okay slider and curve to boot. Maybe the key to his success this year has been using the fastball at a career-low rate. It's certainly helped push his swinging strike rate into a very useful territory, and we're now talking about a robust enough sample to start believing in his strikeout rate. Why not believe his home run rate can return to league average (now 16.7%) and that his xFIP (3.25) is more indicative of his future than his ERA?

Jeremy Hefner can hit home runs, but he doesn't have strikeout stuff. Or ground-ball stuff, really. Or great control, outside of this year. And Chris Schwinden is even worse. Maybe the back end of this rotation really is iffy. It's enough to make a fan start daydreaming about Matt Harvey and Zack Wheeler.