Patrick Corbin’s Dominant Stretch

If you’re just looking at the full season results, you may not be aware of how fantastic Patrick Corbin has been. In his last 14 starts, he has posted a 2.69 ERA and 3.47 SIERA, reminding us of his breakout 2013 season. After missing the entire 2014 season recovering from Tommy John surgery, Corbin picked up right where he left off when he returned in 2015, posting a 3.60 ERA/3.44 SIERA over 16 starts. But then he suddenly fell apart last year as his control deserted him, he was afflicted with gopheritis, and his ERA ballooned to 5.15 as a result. And now, the Corbin with sterling control and the wicked slider is back.

Conveniently, his dominant stretch of 14 starts is essentially half of his season, so let’s split his stats into his first 13 starts and his last 14 starts to search for any process change that stands out.

For his career, Corbin has essentially been a two-pitch pitcher, relying heavily on his wipeout slider to go with his fastball, only occasionally mixing in a changeup. That hasn’t changed this year, except for the degree with which he has leaned on that slider. Previously, his high slider usage was 29% in 2015, which is surprising since he was just returning from major elbow surgery. Now, he has upped that even further, and during his dominant stretch, has thrown the pitch even more frequently, just about 40% of the time! That ranks second to just Chris Archer in slider usage. Throwing your fastball less often and your best pitch more often is usually a good strategy and should lead to an increase in strikeout rate. It doesn’t seem optimal for long-term health, especially after elbow surgery, but we’re less concerned about that.

So this seems like a pretty obvious explanation for his recent success. Then again, he was nothing special earlier in the season even with a slider percentage well above 30%, which at the time was a career high. So who knows.

And there you have it, nearly everything yellow in that second set of starts. Corbin has induced a couple of more grounders instead of fly balls, which in a favorable homer park and a record setting home run environment, is a darn good thing. Yet even with the fewer flies, he has still managed to increase his pop-up rate. Yes, that percentage is out of flies, so technically fly ball rate has no effect. However, there is a strong correlation between FB% and IFFB% — fly ball pitches tend to generate a higher percentage of pop-ups than ground ball pitchers.

Check out the stark difference between his Soft%/Hard% in each time period! Whatever changes occurred, whether mechanical, or something else, made it a lot more difficult for batters to tee off on him. His O-Swing% even spiked, and I would guess that means that batters were fishing for his slider off the plate more often. He was throwing far more first pitch strikes, and because he was inducing swings off the plate, his SwStk% surged. It all sounds so simple — throw your best pitch more often, throw more strikes, and use your voodoo magic to get the batter to swing and miss.

It’s a clean sweep! Because of that increase in strikes thrown and whiffs induced, his strikeout rate has reached levels never before enjoyed over a full season. His control has returned to pinpoint status. Oddly, his BABIP remains inflated. Though a quick look at UZR/150 reveals why that may be — the Diamondbacks sit third to last in the metric at -5.2. Although Paul Goldschmidt has played a fine first base, Jake Lamb has been terrible at the hot corner, while their three-headed shortstop monster of Chris Owings, Nick Ahmed, and now Ketel Marte, all sport negative UZR/150 marks, with Owings significantly negative. And Brandon Drury at second has been just about average. So Corbin is clearly getting no help from his defense.

His HR/FB rate during the second time period is actually below the full season league average, which is surprising given his home park. Somehow, he has managed to strand nearly 80% of his runners during that time frame, despite the inflated BABIP and a high HR/FB rate (even though it’s below average, it’s still well above marks we had gotten used to several years ago, and that usually correlates with a lower LOB%). All told, his skills improvement has led to a near full run drop in SIERA.

It’s hard to imagine that high slider usage is sustainable, but Corbin has still performed well in the past even when his slider rate was in the 20% range. Now fully recovered from TJ surgery, his velocity is fine and control is back. He should continue to be a mixed league asset the rest of the way.