Patrick Corbin Got Better, Then Worse, Then Better

Five years ago, 23-year-old Patrick Corbin put together a very promising season. In more than 200 innings, Corbin’s 3.41 ERA and 3.43 FIP both represented solidly above-average marks, while the 3.5 WAR he recorded pointed to what was a coming-out party for a player who never featured heavily on top-prospect lists. Unfortunately, the party didn’t last: Corbin underwent Tommy John surgery before the 2014 season, and despite a good showing after his return in 2015, he took a step back in 2016 before producing a decent campaign last year. This season, somewhat surprisingly, Corbin has been one of the best pitchers in all of baseball despite having lost some velocity on his fastball in May.

After just two of the left-hander’s starts this season, Jeff Sullivan noticed that Corbin was using a slider more often — that he was, in fact, using two different sliders — to the exclusion of the fastball. As the season has gone on, the slower slider has been classified often as a curve. Despite the slower speed, however, it still features the same movement as the slider. To consider the similarities of the pitch, consider the graph below, which shows the difference between slider movement and curve movement for all qualified pitchers who throw each pitch at least 5% of the time.

Most pitchers’ curves feature more drop than their sliders. The two pitches typically feature different horizontal movement, as well. On average, the difference is about four inches vertically and three inches horizontally. For Corbin, though, the horizontal difference between the pitches is less than an inch, and the vertical difference is almost nothing. Corbin generally uses the curve on the first pitch of an at-bat, with more than half of his curves coming on the first pitch and nearly three-quarters of his curves coming with no strikes, per Brooks Baseball. It’s a pitch he uses in the strike zone when the batter is probably expecting a fastball. The curve helps Corbin either stay ahead or get back even in the count, and still gets a decent 13% whiff rate because of the timing.

In an era that has seen pitchers move towards the four-seam fastball and away from the sinker, Corbin has actually gone the opposite direction. Over the past two seasons, the lefty has cut his four-seam usage in half and shifted most of those pitches to his best pitch, the slider. He’s also shifted away usage from his change, which has meant doubling the combined usage of the slider and curve to nearly 50%, while his two fastballs have essentially been relegated to secondary offerings.

Using the slider more might seem like the obvious move for Corbin — and, clearly, it has worked for him — but it isn’t as easy to pull off as one might think. Pitchers who throw more sliders also typically throw more pitches outside the zone. This is where Corbin has thrown his sliders this season.

That’s a pretty high concentration of pitches outside the strike zone — and, in fact, nobody pitches more outside the strike zone than Corbin, who’s 38% zone percentage is the lowest in MLB. To make that work, Corbin has to induce a lot of swings outside the strike zone. While that’s certainly the case — his 37% O-Swing rate ranks third in baseball behind Carlos Carrasco and Jacob deGrom — that still means hitters are taking the other 63% of pitches outside the zone. In theory, if batters never swung at all, they would walk in nearly half of their plate appearances against Corbin. That theory doesn’t translate to practice, because Corbin does a good job getting strike one.

The graph below shows the percentage of pitches in the strike zone along with first-strike percentage for all qualified starters.

Patrick Corbin is way better at getting first-pitch strikes than most pitchers — even if they all throw in the strike zone much more frequently than he does. That has a lot to do with how Corbin approaches the plate depending on the count. The graphs below show where Corbin pitches depending on the count.

By getting so many first-pitch strikes, he limits the number of pitches he has to throw in the middle of the strike zone. As a result, he can use his curveball to keep hitters off balance, while his ability to throw the slider at any time is always going to be a plus. The great slider and its 29% whiff rate is what makes this possible, but getting ahead in the count without being too predictable helps the slider achieve the best possible results.

Now, about that drop in velocity…

The loss of arm speed Corbin exhibited in May appeared to be a harbinger of potential issues for the Diamondbacks’ lefty. A loss in velocity can often foreshadow a trip to the disabled list. More than three months later, though, Corbin has been pitching well despite losing several ticks off his fastball. For the season, Corbin has a 2.46 FIP that has resulted in a 4.7 WAR, a figure that ranks sixth in all of baseball. His 3.15 ERA is also very good. He continues to strike out a lot of batters, limit walks, and his solid ground-ball rate helps keep his homers down. When we look at Corbin’s first month compared to the rest of the season, we see the strikeouts are down some and the walks are up slightly, but he’s still been very effective overall.

Corbin has given up some harder contact the last few months, but his home runs have also gone way down. I think it is fair to say that velocity does matter for Corbin, but he’s still a very good pitcher even when working at something less than the top of his range. Perhaps most encouraging is that he’s had his three highest average game velocities since April in his four starts since the All-Star Break. Probably not coincidentally, Corbin has pitched great, striking out 34 batters against just two walks in 26.1 innings across four starts. It’s possible having a week off recharged his arm a bit. His velocity still wasn’t up to April levels, but his results certainly were. While the velocity increase is good news, it’s even better to know that if it drops a little, Corbin will still be a very good pitcher.