Yusei Kikuchi Is Keeping the Ball in the Yard for a Change

The Toronto Blue Jays have devoted huge resources to their rotation, spending a first-round pick on Alek Manoah, doling out huge free agent contracts to Chris Bassitt and Kevin Gausman, and trading the farm for José Berríos. (And then giving Berríos a huge contract extension as well.)

But Toronto’s best starting pitcher over the past month — and in a three-way tie for the best pitcher in all of baseball, by WAR — has been Yusei Kikuchi, the guy who couldn’t stay in the rotation a year ago.

Kikuchi was hardly a bargain bin pickup himself; Toronto spent $36 million over three years to sign the Japanese lefty away from Seattle. But his first season north of the border couldn’t have gone worse. Kikuchi posted a career-high ERA- of 134, and his underlying numbers showed that he deserved every bit of it. Kikuchi struck out 27.3% of batters, a career high, but he walked 12.8% and allowed a HR/9 rate of 2.06. It’s like he was trying to piss FIP off.

Among the 140 pitchers who threw at least 100 innings last year, that walk rate was not only the highest, but it beat the second-worst walk rate by 1.3 percentage points. Kikuchi’s HR/9 ratio was the second-worst. Considering that he was swimming in the two things a pitcher most wants to avoid, it’s surprising that Kikuchi’s results and peripherals weren’t even more abysmal.

The bad times continued until the end of May this year, but since Memorial Day or so, Kikuchi has stopped walking people and has kept the ball in the yard:

Bully for him. Problem solved, let’s all go home.

Or, we could try to figure out how he’s doing it. Cutting the walk rate is a big thing, obviously, and Kikuchi is throwing more first-pitch strikes and working in the zone more than he did in 2022. Other than the walk rate, the most notable change in Kikuchi’s fortunes has been a decreased quality of contact on balls in the air. Here’s a month-by-month breakdown of the fly balls Kikuchi has allowed as a Blue Jay, with the percentage of fly balls that left the bat at 95 mph or faster, or were projected to travel 330 feet or more:

Kikuchi’s opponent wOBA on fly balls last year was not only the worst in baseball out of 415 pitchers who allowed at least 30 batted balls of that type, it was the worst by 55 points. Time was, almost every fly ball Kikuchi allowed looked like something piloted by Chuck Yeager. Now only some of them look that way. As a result, the second-most homer-prone pitcher of 2022 is now un-dingered-upon in his past five starts, the second-longest streak of his career. He’s still allowing more damage than average on fly balls this season, but it’s livable now:

How is he doing this? Well, Kikuchi has changed his arm angle slightly to extend his arm farther to left. Here’s a scatter plot of Kikuchi’s average release point by month since he joined the Blue Jays, with the months of 2023 in red:

And that change is even more pronounced than the graph makes it look, because in 2023, Kikuchi has introduced a new pitch, a curveball, that’s he’s throwing almost 20% of the time and releases about six inches closer to neutral than his fastball.

If there’s a story to Kikuchi’s 2023 resurgence, it’s his revamped breaking ball repertoire. Last month, Nick Ashbourne tied Kikuchi’s corner-turning performance to the curveball’s evolution from a show-me pitch to a genuine weapon. And this spring, Sportsnet’s Arden Zwelling detailed the process behind Kikuchi’s new slider, which is coming in two ticks harder this year than last.

In 2022, Kikuchi was a two-pitch guy against lefties, and did quite well. Unfortunately, due to generations of social engineering that are beyond the control of one baseball player, most people in the U.S. are right-handed. Specifically, most baseball players. And against righties, Kikuchi got wrecked, to the tune of a mid-.400s opponent wOBA on his two most commonly used pitches:

Adding the curveball has given batters a new velocity band to look out for; last year, Kikuchi was throwing his fastball at an average velocity of 94.9 mph, his slider at 86.4 and his changeup at 87.0. This year, the fastball is averaging 95.3 mph, the slider 88.9, and the changeup 88.7, while the curveball comes in at a comparatively Entlike 82.9.

I’m convinced this new pitch is working for him, but I’m less convinced it’s actually a new pitch. This is Kikuchi’s fifth year in the major leagues, and only once has he kept his repertoire the same from one season to the next. This is not the first time Kikuchi has used a curveball and a slider at the same time; he did that in 2019 before he introduced a cutter and junked the deuce.

But that wasn’t the same curveball he’s throwing now. In fact, Kikuchi’s current curveball resembles his 2020-21 slider more than his 2019 hook:

Kikuchi has thrown 344 curveballs this season. I went back and found the median 50% for that pitch in velocity and movement. That means a velocity of between 82 and 85 mph, with between 39 and 47 inches of drop and between four and eight inches of glove-side break.

Kikuchi has thrown 153 breaking pitches that meet those criteria in his career: 70 curveballs, all thrown this season, and 83 sliders, all thrown between 2019 and 2022. What I said a couple paragraphs back about the new curveball and the old slider being the same pitch was a little glib; the pitches marked as curveballs spin, on average, about 140 rpm faster than the sliders, though there is some overlap. Moreover, this year’s curveball has more average horizontal break than any slider Kikuchi has ever thrown. These are probably two distinct pitches with similar movement profiles.

But I’m not sure saying that Kikuchi “added a curveball” is the right way to look at this. This is the second season in which Kikuchi has averaged about 95 mph on his fastball, offset by a breaking ball with an average velocity of about 83 mph. The other year that fit those criteria was 2021, when he was an All-Star.

What changed between 2021 and 2022? Kikuchi (for all intents and purposes) stopped throwing his cutter. And as much as I’d love to go on another rant about how pitch classification is an inexact science and Kikuchi’s old cutter is now a slider and his old slider is now a curveball, that’s not the case. The cutter, may it rest in peace, was a low-90s pitch with much less break than Kikuchi’s current upper-80s slider. But it seems like Kikuchi’s low-80s breaking ball, whatever it is or whatever it’s called, needs a harder, tighter sibling in order to be effective. Kikuchi didn’t have that last year, and he got crushed. Now that he’s got it back, he’s on the best run of his career.