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Why is Nestor Cortes struggling to go deep into ballgames?

Nestor has been Nasty through four innings, but has fallen apart in the fifth and sixth lately.

MLB: Tampa Bay Rays at New York Yankees John Jones-USA TODAY Sports

The Yankees plan heading into spring training was fairly straightforward: ride a dominant rotation headlined by Gerrit Cole and offseason acquisition Carlos Rodón and a deep bullpen that contained several top relievers even if it lacked a true closer, and hope that this top pitching staff would compensate for a lineup that contained more questions than a two-year-old who just learned the meaning of “Why?”

Obviously, that plan has not come to fruition. Sure, Gerrit Cole has looked like an early Cy Young front-runner, but the rest of the rotation has not come to play. Rodón, Luis Severino, and Frankie Montas give the Yankees injured list a better top of the rotation than half the league has on their active roster, and while they’re doing their best, Domingo Germán, Jhony Brito, and Clarke Schmidt are not the equals of a pair of two-time All-Stars and a pitcher who finished in the top 10 in the Cy Young vote. Meanwhile, fan favorite lefty Nestor Cortes has been little better than replacement level, accruing 0.5 fWAR (and Baseball-Reference pegs him as below replacement level, with a -0.1 bWAR) as he posts an ERA of 5.53.

While some level of regression would not be totally unexpected, the drop that we’ve seen this year has been much sharper than anyone could possibly have accepted. But what exactly has been behind his struggles? The beginning of the answer may lie in his season splits.

The trend is clear. From the first to the fourth inning, Cortes has given up a grand total of eight runs in 32 innings; from the fifth inning on — just 10.1 total innings — he has surrendered 13. On top of that, all four runs he gave up in the first inning came on April 30th, when the Texas Rangers strung together two walks, a single, and a grand slam with one out. While, obviously, you can’t ignore this inning, it does nonetheless reinforce the trend that Cortes has been his dominant 2022 self early in the game, but once the pitch count starts getting elevated, hitters begin to tee off — once he’s thrown 51 pitches, in fact, hitters have teed off against him like they’re Aaron Judge (who, at time of writing, has a .875 OPS).

So the solution ought to be simple: once Cortes has gone twice through the order, get ready to pull him. Unfortunately, it’s not certain that the Yankees have that luxury right now. Yankees starters have gone more than six innings just seven times this year; Gerrit Cole has done it four times in eight starts. Only five teams have leaned on their bullpen more than New York has so far this season. Because of this, it’s imperative to at least attempt to get more depth out of Cortes — which means it’s critically important to discover the cause of his struggles.

One of the biggest stories so far this season has been the pitch clock. While much of the early discussion focused on the shorter game times, fans and journalists have begun in recent weeks to discuss the possible impact that the clock has had on individual performance. Yesterday, an Associated Press article highlighted the increase in blown saves this year, attributing it to relievers rushing in stressful high-leverage situations. Although this isn’t relevant for a starter like Cortes, it’s fair to wonder if the pitch clock might be leaving him more “gassed” by the fifth inning than he had been last year.

How do you “quantify” fatigue? There is no one-to-one stat correlation, but for the sake of argument, let’s look at fastball velocity and spin rates.

In order to get a “baseline” for how Cortes looks like when he’s at his best, let’s take a look back to what is, according to GameScore, Cortes’s best start of 2022: his outing on October 1st, during which he allowed just one hit in 7.1 innings while striking out a season-high 12 hitters (resulting in an 86 GameScore). Here is his velocity, split up by pitch type, over the course of the evening.

From this chart, there seemed to have been no noticeable difference in velocity on the fastball over the course of the game. The only real visible trend is that the velocities were more consistent on a pitch to pitch basis early on. So let’s dive into spin rate a bit. Here are all the pitches that Cortes threw in the first that day: as you can see, most of the fastballs hovered around 2200 rpm, reaching as low as 2097 and as high as 2292.

Now, for the seventh inning (his final full inning):

Seven innings in, the spin rate on Cortes’ fastball is still hovering around 2200, although with a higher margin on each side. This time around, it bottoms out at 2046 rpm, but he’s able to push it to 2311. To some extent, this shouldn’t be too much of a surprise, as rare are the days in which a pitcher is more dominant than Cortes was.

Now, let’s look at his start this past Saturday, in which Cortes allowed one run over the first four innings before melting down in the fifth. We’ll start again by looking at velocity over the course of the game.

Once again, there’s no noticeable drop-off in fastball velo over the course of the start. Now let’s look at the spin rate, in the second inning (he only threw six pitches in the first) ...

... and in the fifth ...

Once again, there’s little noticeable difference in spin rate over the course of the game.

So, if fatigue isn’t causing his pitches to not be as sharp, what could it be? While it would require a bit more digging to say anything for certain, my gut would be his command later in games is slipping. Here’s his pitch chart from the fourth inning on Saturday ...

... and here’s what it looked like just one inning later.

This is just one start, and even more specifically, just two innings in one start. Nonetheless, it seems to me that Cortes started to lose a feel for his fastball in the fifth. We see him lose the zone a bit back on May 8th against the A’s ...

... and on April 30th against the Rangers.

Now, of course, it’s still fairly early in the season. This may simply be a blip on the radar, much like we saw last June, when he gave up four runs three times in six starts. Nonetheless, it is something that bears watching in the coming weeks, because if the Yankees want to climb out of the hole they’ve been shoveled into by this deep American League East, they need Nasty Nestor to be, well, Nasty for more than just four innings.