I was so wowed by last night’s performance by Patrick Corbin that I set out this evening to write it up.  Before completing the below, Jeff Sullivan of FanGraphs posted about the 10 most unhittable pitches this season – Corbin is the only starter in there.  You should really take a look at that, as I won’t republish his findings here.  Suffice it to say, his slider has been…pretty good.

It’s no secret that Corbin has taken an enormous step forward this year in terms of performance, but I was curious to see whether it had to do with pitch selection or with improved stuff.  As a shortcut, I compared last night to a single performance last year.

Corbin’s best start last year was probably when he took the mound against the Giants on September 16.  He had a six inning scoreless start at the beginning of August, but on Sept. 16, Corbin lasted a full eight innings, issuing only one free pass and letting up just two earned runs.  The biggest thing that stands out between that start and last night is the strikeouts – Corbin got 5 Ks in that start last year and 10 last night.

In fact, Corbin had a mere 7.23 K/9 overall last year.  It’s up to 7.83 K/9 this year, but that doesn’t tell the whole story; Corbin has faced less hitters per inning this year (3.99 Total Batters Faced per inning) as compared to last year (4.24 TBF/IP).  He’s struck out a higher proportion of guys this year (21.8% of batters faced) than in 2012 (18.9%).

Corbin’s BABIP in 2012 was a relatively high .317, whereas this year balls in play have turned into hits at a .256 clip.  That’s a low enough rate to make it fair to ask whether he’s been lucky this year.  If his slider has been as filthy as it looks on television, however, it may be that hitters are just getting less good contact off of that pitch.

Thanks to BrooksBaseball.net, we can see all kinds of amazing data on Corbin’s Sept. 16, 2012 start and his start last night.  One of the principal differences that leaps out is pitch selection.  Since the pitch statistics were coded by different sources, I’m not sure if the pitch type determinations for fastballs are directly comparable – Pitch Info had 19 4-seam fastballs and 29 2-seam fastballs in 2012, whereas the MLBAM algorithm found 54 2-seamers to just eight 4-seamers last night.

One thing we can definitely compare, though, are the changeup and slider choices.  In the 2012 start, Corbin threw 25 changeups – good for 27% of his pitches.  He got plenty of sliders in there, too – 20, or about 21%.  Flip back to last night, though, and you’ll see that just four of Corbin’s pitches were changeups (>4%), while he threw a staggering 37 sliders (36%).

Last night was an extreme example, but Corbin has moved away from the change to the slider this year as opposed to last.  How his pitch selection has broken down, courtesy of FanGraphs:

Year Fastball% Slider% Changeup%
2012 68.9 16.4 14.7
2013 67.6 22.4 10.0

The shift in approach isn’t enormous, but when you consider that Corbin has already thrown 2,467 pitches this year… that’s a lot more sliders.  And if last night was any indication, more sliders might mean more success, because it’s just so damn unhittable.  (side note – I’m no apologist for “wins” as a statistic, but you do wonder sometimes if a team battery changes how they select pitches based on the score – remember, Corbin was protecting a one-run lead for most of last night’s game).

How unhittable?  Thanks to BP, I can tell you that more than half of the time hitters have swung at Corbin’s slider, they’ve missed it completely.  Among pitchers to have thrown at least 200 sliders this season, Corbin’s whiff/swing rate has led the pack at 54.35%.  Consider that he’s only gotten a whiff/swing rate of 13.81% on the 4-seam and 11.61% on the sinker.  Sure, he has a 30.91% whiff/swing on the changeup – but one wonders if the jump from the 22.32% rate he had last year has a little to do with Corbin throwing it less (and it being more of a surprise).

The slider can’t be as much of a surprise this year, but it’s still jumped to that 54.35% from last year’s 46.67% whiff/swing rate.  It seems like the swings and misses Corbin has gotten this year has a lot to do with the slider.  And there have been a lot of whiffs – Corbin has a Swinging Strike rate of 11.1% per FanGraphs, good for fifth in the NL among qualified starters, behind only Matt Harvey, Cole Hamels, Mat Latos and Clayton Kershaw.

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