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Keynan Middleton has come full circle

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The former closer is flashing current closer stuff

MLB: Seattle Mariners at Minnesota Twins Bruce Kluckhohn-USA TODAY Sports

Keynan Middleton was supposed to be the Angels’ closer of the future. So you can imagine that it was pretty disappointing when he went down with Tommy John surgery, and even more disappointing when he came back as a shell of the pitcher he was before. The Angels, apparently, didn’t consider it a priority to bring him back to their middling bullpen, which isn’t exactly something that speaks well to Middleton. Perhaps, then, the Mariners may have seen something that they could unlock.

For me, I saw a few different things. I took a bit of a leap in December when I wrote that Middleton not only could use an adjustment in pitch mix, but also that his slider could use a little tweaking. As I saw it, his slider didn’t render enough chases out of the zone, so he would need to shave some velocity off of it or add more drop to do that.

To date, he may have achieved one of those two things, and the change in question was the harder one. Let’s take a look at Middleton’s pitch movement and velocity since 2019, by year:

Slider, labeled in green

Now, I’d have left Middleton’s other offerings out of this graphic, but I think it’s instructive to how his slider differs from his fastball and changeup in terms of velocity and movement, because pitches don’t exist in a vacuum. In 2019, Middleton didn’t pitch much, but he had a good slider when he did. His fastball velocity just wasn’t there. In 2020, he got his fastball velocity back, but with that came a bump in slider velocity, too, and he didn’t get the drop he needed on his slider. That led to a pitch that had some success in the zone, but one that also failed to draw swings outside of the zone, which is crucial in two-strike counts.

In his first three games, Middleton came out showcasing middling velocity that was an issue in 2019 and then picked it up in the next couple of games after that. Then he did this:

Red line to allow for frame of reference

Middleton’s average fastball velocity over his career is skewed from the latter half of 2018 and 2019, but his outing on the 24th just eclipses his career average, which is a big deal for someone with subpar command and a secondary pitch that falls well short of elite. Now, perhaps Middleton had a little extra adrenaline pumping that day, but that feels unlikely while pitching in the eighth inning of a game that wasn’t especially close. If we’re to assume that his velocity holds, then that allows us to shift our sights to Middleton’s slider.

On the surface, it’s not all that clear that Middleton has made any significant tweaks to his slider. By active spin percentage, his slider has remained constant from last year. It’s slower this year, and it’s getting more drop as well, but that has to do with his overall velocity. As we saw his fastball velocity climb to 96 mph during his last appearance, his slider also climbed to 86 mph, which is about as hard as he threw last year.

First, the spin direction of Middleton’s pitches in 2020 upon release, and then once they reach the plate:

What you’re seeing here is, because Middleton gets a fair amount of gyro spin (i.e., spinning like a bullet) on his slider, the spin direction of his slider varies a fair amount. On average, the spin direction of Middleton’s slider is at 12:00, if you were to look at a clock. When it arrives at the plate, though, its spin direction is more towards 11:00. This isn’t uncommon, but important to note.

And then again, but this time, Middleton’s 2021 offerings:

Despite similar movement on the whole, what you’re seeing here is pretty different. Upon release, the spin direction of Middleton’s slider has shifted all the way to 10:30, and by the time it arrives at the plate, its spin direction is at 9:15. And so, we’re seeing the spin direction of his pitches changing, but the gap between the spin direction of his slider upon release and when crossing the plate has widened. You may also notice that the variability of Middleton’s slider’s spin direction has increased as well.

Oftentimes, that speaks to the effects of seam-shifted wake, meaning that the orientation of the ball can dictate how air interacts with the seams, and thus changes the movement of the ball in flight. We talk about pitch deception a lot in the context of pitcher mechanics and pitch tunneling — and seam-shifted wake is related to the latter — but this is a way of being more deceptive by a pitcher’s offering being a different pitch at the beginning of its flight compared to the end of its flight.

And so, for Middleton, he may not have made any tweaks to his slider that are salient to a layperson — it, for the most part, would lead you to believe it’s the same pitch — but we may have enough changes here to suggest that it can be a stronger pitch than it’s been in the past.

The returned fastball velocity is one thing — Middleton probably needs it if he hopes to be a solid reliever. But an improved slider is his second prerequisite if he hopes to exist in the form of a potent, dominant reliever. Kendall Graveman’s emergence as a potentially elite fireman has given the Mariners’ bullpen an awful lot of flexibility. If Middleton continues to surge with his fastball velocity and slider, he may add to that. And within a matter of weeks, that may mean putting Rafael Montero out of a job.