Un-Athletic

It doesn’t matter what perspective you prefer, the Yankees trip to Oakland was not a success. To some, it was a catastrophic failure. To others, it was a chance to get a good look at a team that will ultimately stand between the Yankees and a chance to compete for a World Series birth.
Personally, I don’t feel the Yanks’ trip to Oakland this week was the end of the world. I’ll also admit I’m a glass-half-full guy, but it’s easy to be when the Yankees still have one of the best records in baseball.
That being said, there are still serious concerns regarding the health, performance, and cohesion of this club; and at the epicenter of that criticsm are Gary Sanchez and Luis Severino.
The scary part is that I think Sanchez is closer to being back to what we can expect than Severino. I feel like it is only a matter of time before his timing at the plate returns, and when it does, his defensive miscues will become less glaring. Still, former manager Joe Girardi had some interesting insight on MLB Network regarding Sanchez’s catching mechanics:
The point is, the narrative for Sanchez changes when he starts to hit. No, he hasn’t produced thus far in 2018, but a single unperforming, injury ridden season is not enough for me to close the book on Sanchez’s career (or even the rest of 2018).
Severino is far more frightening to me. Why? Well, Luis Severino still throws hard, hasn’t been injured, and hasn't been pressured to succeed in anything besides pitching. I’ve attached some charts to bring this all to life:

This is a simple chart that illustrates how Severino’s ERA has jumped over the past 15-or-so starts.

This chart illustrates the usage of Severino’s Changeup and his Slider over the course of the season. What you can notice is their indirect relationship: the more Sevy goes the changeup, the less he throws his Changeup (makes perfect sense, there are only so many pitches in a game).
The issue is that Severino’s Changeup is not good enough to have it match his Slider usage. The Batting Average against Sevy’s Slider is .190 compared to a staggering .271 against the Changeup (Per Fangraphs).
In addition, Severino’s fallen into some bad luck, particularly with his Slider. The BaBPIP of .297 for Severino’s slider is 100 points higher than the batting average, even though the value of his Slider still ranks 8th in all of MLB, so expect a regression on that success against that pitch (Per Fangraphs).
The good news for Severino is that batters will keep swinging, even if he returns to throws his superior pitch more of the time. In fact, they’ll swing more; with the swing percentage of his Changeup at 45.7% compared to the 47.8% on his Slider (Per Fangraphs).

Okay last chart. I promise.
This one won’t be hard to compute, because it’s pretty much a combination of the past two charts. The yellow and dark blue lines are Slider and Changeup usage, the light blue line is ERA, and the red line brings the additions of fastball usage.
Now, I’m going to backtrack slightly on what I argued just before. Severino should still find a way to throw his Slider more, and as you can see, that most closely correlates with Sevy’s ERA low on the season. However, maybe not at the expense of just his changeup. The 4-Seam-Fastball is always going to be the easiest pitch to hit, but it’s also an important and reliable weapon that pitchers need to frequent. That being said, I think Severino would be smart to decrease the usage of both his Changeup and Fastball very slightly, so he could throw his Slider more frequently. Quite simply, if you look at the chart, the pitch usage that most directly correlates with the ERA graph is Fastball usage.
We’re going to step away from the numbers to wrap this up. I think Severino has lost a lot of confidence in his slider due to some rough luck. As a result, he doesn’t throw it with the same confidence, conviction, or consistency that he did earlier in the season. In this day of baseball, 100mph doesn’t blow hitters away anymore, and I think Severino has tried to hide behind his velocity over the past 10–15 starts.
His poor luck with his Slider has also lead him into exploring his changeup more. I don’t hate this move from Sevy, because it will ultimately be a pitch he needs to develop in order to become a top-flight ace, but the pitch simply isn’t there yet. Severino should take that next step in the offseason, but work what has been more effective while the Yankees are still chasing down a pennant.
To bring it full circle: Gary Sanchez has to instill confidence in this staff to throw wipeout off-speed pitching (that presumably hit the ground), and Severino has to be okay with throwing the shit out of his Slider. If Severino, or any other pitcher on the staff, isn’t comfortable throwing their secondary pitches, it’s going to be a tough finish for the Yankees starters.
