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A Look at the Improvements of Nestor Cortes in 2021

By Chris O’Connor

August 13, 2021


Nestor Cortes Jr. was drafted right out of his Florida high school in the 36th round by the Yankees in 2013. At 5’11”, 210 lbs, a less-than-ideal physique, and a fastball that maxes out around 91 miles per hour, Cortes was never a hyped prospect. Subjectively, I like watching him pitch because he seems to understand his physical limitations and compensates by constantly changing his windup and throwing angle in order to get guys out. After debuting in rookie ball in 2013, he slowly worked his way through the minor leagues. Then, after being selected by the Orioles in the Rule 5 draft after the 2017 season, he finally made his big league debut in 2018. He was designated for assignment that April after struggling and signed back with the Yankees, but he would not reach the majors with the club until 2019. That season, in a long relief role, he went 5-1 but struggled with a 5.67 ERA in 66.2 innings. He was then traded to the Mariners for international bonus pool money, struggled in 2020 with Seattle, and again signed with the Yankees in the offseason. He has broken out thus far in 2021 with a 2.70 ERA in 43.1 innings as he has alternated between spot starts and long relief. Still just 26 years old and under team control through 2025, there are two questions that need to be answered: what has changed for Cortes and is this mini-breakout real and sustainable?

Because he only threw 7.2 innings for Seattle in 2020, it would be more helpful to compare Cortes’ 2021 to 2019 when he was with the Yankees and had a similar workload. Cortoes is throwing his four-seam fastball about the same percentage but is using his curveball more and slider less: his curveball usage has risen from 4.2% in 2019 to 23.5% this year, and his slider usage has declined from 31.4% to 21.2%. His curveball has indeed improved: after batters hit .615 against it in 2019, they are at .250 against it this year. Baseball Savant rates it as about an average curveball, which is certainly an improvement over 2019, but even that may be underselling it: the expected batting average against it is just .173, indicating that he has been unlucky here. The big difference, however, seems to be the improvement of his four-seam fastball. Even though his usage has stayed relatively similar to 2019, its effectiveness has been startling. Cortes throws his four-seam fastball 42.8% of the time, making it easily his most-used pitch. The same was true in 2019, when batters hit .264 and slugged .549 against it. This year, batters have hit just .152 and slug .212. His velocity is up from 89.6 mph to 90.5 mph, but his spin rate is nearly identical. It appears that his fastball itself has not changed much, but perhaps increased deception, slightly higher velocity, and a more difficult adjustment for hitters who have to be ready for his curveball have all added up to complete a remarkable transformation for the pitch.

Is this performance sustainable, or is it more of a small sample fluke? There are a few ways that this can be determined. For one, his xERA of 2.75 and 3.22 FIP tell the story of a pitcher who has been really good. He does a good, if not great, job of limiting hard contact: his hard hit rate and average exit velocity are in the 61st and 59th percentile, respectively. The good/bad news is that both of these are up from 2019, meaning he allows a high percentage of hard hits and a higher exit velocity. The bad news is that, obviously, it is not good for pitchers to allow harder contact more frequently. The good news is that, despite this, he has been excellent overall, and his advanced stats do not suggest that it is too fluky. It appears, ultimately, that Cortes has become more of a 2021-style pitcher, or as much as one can be with a 90 mph fastball. His strikeout rate is a career high 26.4%, up from 23.2% in 2019. He is also walking batters at a career-low rate, but pitching up in the zone to get more strikeouts has led to Cortes allowing more fly balls and less ground balls. So far, that has not been a problem because his 7.5% HR/FB ratio is in the top-30 in the league among pitchers with at least 40 innings. Similarly, his BABIP has sunk from .321 in 2019 to just .264 in 2021, and these two measures explain why other metrics that view pitchers having less control over home runs like SIERA (3.84) and xFIP (4.18) are less bullish on his breakout. This suggests that he has indeed had luck on his side, but even accounting for some regression in these aspects, Cortes has shown that he can be an effective innings-eater.

Increased effectiveness of his four-seam fastball and adding a curveball as a regular part of his repertoire have helped Cortes really step up when injuries shredded the pitching staff. Cortes most likely has been somewhat lucky in allowing just 4 home runs and relatively few hits on balls in play, but perhaps he has adapted to the de-juiced ball and been helped simply by not pitching with the rabbit-ball of 2019. Compared to another Yankee pitcher who has broken out in 2021, Cortes’s profile has mostly been the complete opposite. While Jonathan Loaisiga has seen his strikeouts drop but compensates by allowing more ground balls, Cortes is striking out more batters than ever before and is relying more on fly balls turning into outs. Even if some of his fly balls turn into home runs, the hits start to drop, and his ERA settles in around 4.00, that would be great production from a spot starter. While I am not sure if I can see him starting playoff games, I can absolutely see him having a big role come playoff time if he can keep up this performance.


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