Yusei Kikuchi could use his best pitch a lot better

I write a lot about pitch mix changes that might benefit pitchers. Most recently, I wrote that Zach Eflin should throw his curveball more. Before that, I wrote that Aaron Civale should throw his curveball more. I write these up a lot because most, if not all, pitchers could stand to benefit from an adjustment in their pitch mix. Some minor, some major. It’s one of the easiest ways to forecast breakouts. I think Yusei Kikuchi is another pitcher who could stand to benefit from an alteration in pitch mix. And maybe that leads to a breakout.

Kikuchi’s progression as an MLB pitcher is well documented. In 2019, Kikuchi was a replacement-level player. In 2020, he completely reinvented himself, but the results weren’t there. Now, this year, he’s made a more minute mechanical adjustment, and he’s continued to fade his fastball. I think there’s something to that.

We should probably familiarize ourselves with Kikuchi’s fastball first. Nowadays, he sits 95 mph, and he touches 97-98 mph plenty. He spins it really well by spin rate and active spin rate, which leads to a lot of fastball ride. This is all really good! When you take a closer look, though, things aren’t so promising.

Since 2020, Kikuchi leads all starters in ball percentage with his fastball. That’s somewhat misleading — he ranks in the 51st percentile in fastball CSW — but that indicates that Kikuchi often struggles with the control of his fastball. More than almost any other starting pitcher, he throws a lot of waste fastballs that don’t come close to the zone. What’s perhaps most damning is that, even when his fastballs are inside of what Baseball Savant refers to as the shadow zone, he doesn’t get chases, and he doesn’t get called strikes. When considering these pitches (i.e., fastballs outside of the zone, but in the shadow zone) by CSW, Kikuchi ranks dead last.

A pertinent interaction I had with Eno Sarris and Max Bay:

By Location+, Kikuchi spots his cutter a touch below average and his slider well above-average. His fastball location is what I’d describe as below-average. Between Kikuchi’s last and second-to-last appearances, there’s a big spike in both Location+ and Stuff+, but it’s much more pronounced by Location+.

If you look at his pitch mix, he was throwing his cutter and fastball both a touch above a third of the time in his outing on April 23rd. During the latter game, though, he upped his cutter usage to 48% while dropping his fastball to 20% usage and maintaining his 20% slider usage. The relationship between his change in pitch mix and an improvement in Location+ and Stuff+ isn’t a faulty correlation. His location graded out better because he stopped throwing his fastball as much and he started throwing his cutter more. He did this in his next two outings, too, and it was his best three-game stretch of the year.

By strikeouts and walks, it’s also one of the best stretches of his career:

Sustaining strikeouts like he has recently is unprecedented for Kikuchi. He’s limited walks well too. The easy solution to me is to continue to fade his fastball. That’s the obvious tweak. Take your best pitch, and throw it more. Simple. But something has to take its place.

His cutter is his best pitch by pVAL, and it’s one the best cutters there is by strike percentage and CSW. Something that has gone relatively unnoticed is that, at 36.6%, Kikuchi’s slider has one of the highest CSWs of all starters since 2020 — inching out Gerrit Cole’s slider, and rivaling Jacob deGrom and Joe Musgrove’s sliders. I’ve already said that his pitch mix isn’t optimal. But he’s not locating his slider as well as he could be either.

There are a number of ways to look at this. One way is that, if Kikuchi has a high chase percentage, he should be trying to get hitters to, well, chase. That means that the zone percentage of his slider shouldn’t be all that high. The two pitchers above Kikuchi in slider chase percentage know how to do this. Alex Wood’s zone percentage is 45.3%. deGrom’s zone percentage is even better at 38.5%. At 50.2%, Kikuchi throws his slider in the zone more than most. He’s using his best whiff pitch like a get-me-over pitch.

Consider the trio’s respective slider locations:

deGrom has really got his slider location tightened up. Wood locates his well too. They both spot their sliders to their glove-side at the bottom corner of the zone extremely well. And oftentimes, they’ll throw them out of the zone. Kikuchi locates middle-middle and at the bottom center of the zone, which has mostly returned positive results. But his slider also gets barreled more than his other offerings. And that’s a direct result of locating it out over the plate.

Kikuchi’s pitch ecosystem itself is flourishing. He has four unique offerings that he can use to keep hitters off-balance. He can get hitters to put the ball on the ground with his cutter and changeup. He’s got a pitch he can get hitters to chase and miss in his slider. Sure, he still needs his fastball to keep hitters honest, but there’s no reason he shouldn’t be able to become even more of a cutter- and slider-heavy pitcher than he already is.

That’ll look like some elevated fastballs sprinkled in:

Some elevated cutters playing off his fastball to steal strikes:

Lots of cutters down in the zone:

Sliders dropped into the zone for called strikes:

And then, most importantly, what I want to see more of. A slider that Kikuchi draws a whiff on, outside of the zone:

Tap tap tap tap...tap. Notice Luis Torrens’ non-verbal cues here. He’s effectively saying, “Keep it down. Bury this.” Kikuchi might have let this drift a little more arm-side than he’d have liked, but when you’re throwing outside of the zone, you have a wider margin of error. Kikuchi holds up his end of the bargain and bounces the slider inches away from Torrens’ target as Gavin Lux waves over it.

There are precedents for fading one’s fastball usage. Corbin Burnes’s fastball usage probably isn’t fair to compare to, given his unicorn cutter. But Yu Darvish and Musgrove feel like appropriate examples. If they can throw their fastballs 24% and 22% of the time, respectively, maybe Kikuchi can stand to shave another five percent or so off of his fastball usage.

I don’t know that any of this is ever incorporated by Kikuchi. He’s made several tweaks so far in his short MLB career, and I can only hope this is one of them. That he’s using his cutter nearly half of the time is good. But maybe it isn’t necessary. In the end, it’s as simple as taking his best pitch in his slider and using it better. Throw it more, bury it more, and you’ve got a pitcher who has a pretty new look. It’s hard to see it not working out for him.