March 29: Patrick Corbin gets the nod for his first career Opening Day start with the Arizona Diamondbacks. Entering his walk year with a career ERA over 4 and a history of inconsistency, his free-agency was not highly anticipated by any means. The 28-year-old lefty was left off of almost every list of top free agents of the 2018-19 offseason.
December 5: Patrick Corbin, the most sought-after pitcher on the free agent market, signs with the Nationals for six years and $140 million. Coming off of a breakout season that saw him finish in the top 5 in NL Cy Young voting, he was pursued heavily by several teams. Ultimately, however, Washington won the bidding war, beating out the Yankees and Phillies. In 2019, the 29-year-old lefty will suit up next to Max Scherzer and Stephen Strasburg in what is now one of the best starting rotations in baseball.
What a difference a year can make. In 2018, Corbin was a completely different pitcher. He made 33 starts, throwing 200 innings for just the second time in his career. He came into the season with a career average of 7.9 strikeouts per 9 innings; in 2018, that number skyrocketed to an elite 11.1. He also pitched to a career-low ERA of 3.15 and an even more impressive 2.47 FIP, suggesting his 2018 performance has even more upside. Among all qualified National League pitchers, Corbin’s FIP placed him second only to Jacob deGrom’s historic Cy Young campaign, and his 6.3 fWAR made him the third most valuable NL pitcher, behind only deGrom and Scherzer.
This unexpected breakout campaign raises some questions: what made Corbin such a different pitcher in 2018? Was there one specific adjustment that made him an elite strikeout machine? More importantly, is this the new Patrick Corbin? Is this level of performance something he can replicate with the Nationals, or will he regress back to mediocrity? To explore these questions, we need to look deeper into Corbin’s pitch selection, his approach to hitters, and the quality of his pitches.
First, let’s look at Corbin’s approach to left-handed hitters:
|Year||Fastball %||Slider %||Sinker %||K %||Opp. OPS|
*data courtesy of Baseball Savant
Throughout his career, Corbin had always handled lefties well with the same repertoire of pitches: fastball, slider, and sinker. Holding lefties to an OPS of just .651 in 2017, Corbin struck out an astounding 31% of the lefties he faced.
As a result, he made almost no changes in his approach to lefties. From 2017 to 2018, his fastball, slider, and sinker usage barely changed at all. While left-handed opponents had a slightly higher OPS in 2018, his strikeout rate remained sky-high (33.5%). So, against lefties, Corbin really made no changes – he didn’t need to.
The real difference for Corbin in 2018 appears when we look at his approach to righties. Prior to 2018, he had always attacked right-handed hitters with four pitches: fastball, slider, sinker, and changeup. He never had much success with this repertoire, allowing an OPS of .830 to them in 2017. That year, he struck out just 19% of righties, averaging less than 7 strikeouts per 9 innings.
It’s here that we find what looks to be the most effective adjustment that Corbin made in 2018: he started throwing a curveball.
|Year||FB %||SL %||SNK %||CHG %||CB %||K %||Opp. OPS|
*data courtesy of Baseball Savant
In 2018, Corbin developed a slow, mid-70s curveball, virtually abandoning the changeup that he had relied on for years. Also notable, Corbin’s fastball usage dropped over 10% as he began to rely more heavily on his other offspeed pitches. Still, the most major adjustment in Corbin’s arsenal was replacing his changeup with a curveball.
These changes were apparently the right ones, showing immediate improvement in his numbers: Corbin held right-handed batters to a minuscule .583 OPS, and his strikeout rate against them jumped by a remarkable 11%. In 2018, for the first time in his career, Corbin was actually better against righties than lefties.
The new pitch was Corbin’s only major adjustment in pitch selection, but a lot more than just his curveball changed. In fact, 2018 saw a general improvement in the performance of all of Corbin’s pitches.
Run Value per 100 pitches*
*data courtesy of Fangraphs
This chart uses Fangraphs’ weighted pitch value stat, which measures the performance of a pitcher’s pitches. By evaluating the run expectancy before and after each pitch is thrown, this metric takes the average run value and scales it up to 100 pitches. For example, in 2018, Corbin’s slider was worth an average of 0.021 runs per pitch, which scales up to 2.1 runs per 100 sliders. So, this chart approximates the average performance of each of Corbin’s pitches.
Here we see why it was a good idea for Corbin to replace his changeup: the curveball just worked better. His changeup was consistently terrible. Corbin only threw 36 changeups in 2018, but by this metric from Fangraphs, it was the worst-performing changeup among all qualified pitchers in baseball.
And as the changeup was largely unsuccessful, its replacement worked much better. Newly developed pitches aren’t often very effective, but Corbin’s curveball immediately paid dividends. At about 0.8 runs per 100 pitches, it far outperformed the changeup.
But also, as we can see, all of Corbin’s pitches were significantly better than in 2017 (besides his changeup). We already know that nothing changed against lefties, which suggests that the change that Corbin made against righties specifically is what sparked the improvement of all his other pitches. In other words, Corbin’s curveball made all his other pitches better.
There are a few important reasons to believe this theory. For one, the slow, mid-70s curve added a different speed to his arsenal. After a complete game one-hitter in April, Corbin commented on his new pitch: “It’s just something I’ve been working with and had some success with… something in the low 70s and just keeps the hitters off-balance.”
Besides the slider, none of Corbin’s pitches are elite on their own. His fastball and sinker average about 90mph and are not much better than league average. So when this slow curveball presented an entirely new aspect of his game, hitters could no longer sit on pitches coming in at 80-90mph. They were kept “off-balance,” as Corbin says, and it gave him an advantage he never had before. While this advantage is an intangible one, it made a very real difference in Corbin’s performance in 2018.
So, what can we expect from Corbin in 2019 and beyond – will he live up to his $140 million contract? After looking at the numbers, it certainly seems like this is the new Corbin. By introducing a completely new pitch, Corbin made some very real changes in his game, which shows that his 2018 was no fluke. He’s always had success against lefties, and his newfound success against right-handed hitters is here to stay.
As for the kind of numbers we can expect from a healthy Patrick Corbin next year, we can probably count on much of the same. My prediction, accounting for some slight regression: an ERA around 3.30, and a strikeout rate 10.5 K/9. Fangraphs projects an ERA of 3.43 and a 9.36 K/9, but I wouldn’t be surprised if we see something even better than 2018.
Looking at the bigger picture, Corbin has now established himself without the high-90s fastball featured by many of the top pitchers in the game, instead relying on an elite slider and good offspeed pitches. This kind of pitcher typically has increased longevity into their older years (in his deal with the Nationals, Corbin is signed through his age-34 season). So, Corbin probably has a good chance at living up to his contract. From what we’ve seen, there’s a bright future ahead of him.
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