Yusei Kikuchi Has Finally Hit His Stride

The wait for Kikuchi to break out might finally be over.

It’s been more than five years since Yusei Kikuchi signed with the Mariners as an international free agent. He had a tough transition to MLB, which led to him reinventing himself that following offseason. He came back in 2020 throwing substantially harder with much louder stuff. Ever since then, we’ve all been waiting for him to break out and use that new and improved arsenal to great effect. 2020 came and went. 2021 came and went. 2022 came and went. It wasn’t until the second half of the 2023 season that we really saw him come into his own as a pitcher. Now he’s back this season having made potentially even more improvements, looking to build off of the most successful run of starts he’s had in his MLB career.

The Fastball

Kikuchi’s fastball is excellent, especially for a lefty. He throws it pretty hard, 95.5 mph on average. That’s the seventh-highest fastball velocity for a lefty starter so far this season. On top of that, it has excellent movement. 17.4” of iVB with 7.7” of iHB is solid, and it plays up further given Kikuchi’s low 5.4’ release height. He also releases the ball with 7’ of extension from the rubber, adding to the pitch’s power and flat plane. Above-average vertical movement coming from a lower slot like this creates the exact type of path you’d expect. It has an excellent +0.7° VAAAA, and a +1.7 HAVAA, meaning it’s an exceptionally flat pitch.

This is why it’s capable of missing so many bats. This kind of power and movement is uncommon, but it’s exceptionally deadly for a lefty. Lefty fastballs are held to a lesser standard as they have a lower velocity on average. So when one is built a bit differently like Kikuchi’s, it stands out more than it would on a righty. He also has the bonus of rising fastballs playing better in platoon matchups than they do against same-handed hitters. This is an excellent foundational piece to an arsenal, and Kikuchi uses it as such.

The Curveball

Kikuchi’s curveball is of the gyro-heavy variety. It favors power over big, aesthetically pleasing movement. It comes in at 83.2 mph, with -3.6” of iVB, and 4.7” of glove-side iHB. Generally what you look for with gyro curves is power and vertical depth while trying to keep the horizontal movement to a minimum. That is what creates that devastating 12-6 shape we’re familiar with on what have recently been dubbed “death-balls”. Kikuchi’s is a little different. His has a bit of horizontal, placing it in between that straight shape and something more slurve-y. You can think of this pitch as something resembling a slider with more depth than you’d expect. If you view it as a gyro curve, you’ll wind up giving it less credit than it deserves.

This is a really solid pitch that he can use against both righties and lefties. It has the depth to get whiffs and ground balls and he locates it exceptionally well. He seems to have a knack for hitting the arm-side corner with it to steal strikes. When it’s not there, it’s usually below the zone getting chases. This is a bit of an unorthodox pitch, but Kikuchi’s ability to locate it helps it play up as a trustworthy secondary offering.

The Slider

Kikuchi’s slider is a bit difficult for me to evaluate. Like everything else, he throws it with power, averaging 89.6 mph. The movement on the surface seems pretty all right, at 4.5” iVB, and 2.3” of glove-side iHB. What makes it tricky is that his low release combined with the lack of elite iVB suppression leaves this pitch in a weird spot. By slider standards, this pitch is seriously lacking in depth both by overall drop and by its VAA-related stats.

However, if you treat it more like a cutter, the results he gets with it start to make more sense. Kikuchi used to throw a cutter that he has since scrapped after losing the feel for it. It got hammered in 2022 and he did away with it. This pitch is kind of the spiritual successor to that one. It’s a bit slower but it has more horizontal movement and depth, allowing it to get that weak contact he’s looking for. His ability to locate it below the zone on the glove side will also help with that, and even garner him some whiffs in the process.

The Changeup

We’ve reached the most frustrating part of Kikuchi’s arsenal. His changeup has the makings of a truly great one. Its movement specs of 7.6” of iVB and 13.8” of iHB at 87.0 mph aren’t what give it promise. That movement at his release is pretty pedestrian. Rather, it’s the way it fits into his arsenal. It has almost 10” of iVB separation from his fastball and it spins on nearly the same axis out of his hand. He sells the pitch brilliantly. Nearly identical releases and spin directions make it impossible to tell which is which out of his hand at first.

Sounds great, right? There’s just one problem. He has absolutely no ability whatsoever to locate this pitch right now. Yes, after I spent the last two sections praising his command of his breaking balls, we come to discover his changeup does whatever it wants to do regardless of where Kikuchi is aiming. This is immensely frustrating and relegates the pitch to the “developmental” label. Lots of potential, but it needs serious refinement.

The Outlook

This isn’t a case like some of the previous articles where I have a lot in the way of suggestions for how the pitcher could be doing better. Kikuchi is starting to look like a finished product out there. He’s got 3 plus pitches, all of which are best suited to dismantling opposite-handed hitters, the type he faces most often as a lefty.

If I had to nitpick and make a suggestion or two anyway, I’d say he could probably stand to be a little bit less aggressive with his fastball. He could aim higher with it, as it catches the middle of the zone a bit more often than I’d like. Overall though, it’s not that big of an issue. His fastball command is better than average.

He’s executing his pitches far better this season which is playing a huge part in what’s fueling his success. His quality pitch percentage is up at 56.3%, which is in the 94th percentile for starters; it’s far higher than it’s ever been for him before. He’s also cut back on mistakes, with his bad pitch percentage at 29.0%, the lowest it’s ever been, good for the 79th percentile. His mistake rate, as you might expect, has also cratered down to 4.4%.

As I said a bit ago, this article is a bit different. This isn’t one about a pitcher who’s on the verge of being great. This is about a pitcher who’s been shoving under the radar a bit, and might finally be the guy we’ve all been hoping he’d become.

Jack Foley

Jack is a contributor at Pitcher List who enjoys newfangled baseball numbers, coffee, and watching dogs walk by from the window where he works. He has spent far too much time on the nickname page of Baseball-Reference.

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