The One-Year Anniversary Of Yusei Kikuchi’s (New) Curveball

Few pitchers have had an up-and-down career in the majors like Yusei Kikuchi. The former Seibu Lions star made the jump from Nippon Professional Baseball to Major League Baseball in the 2018-19 offseason when he signed a four-year, $56MM contract with the Mariners. That deal contained a series of complicated options that allowed the Mariners to pick up an additional three years of control over Kikuchi — with that decision coming after year three of the contract — but also allowed the left-hander the opportunity to opt out if that three-year option was declined.

For much of Kikuchi’s time in Seattle, the four-year guarantee looked regrettable. Kikuchi made 32 starts in his rookie season but posted an ERA north of 5.00 with a lackluster 16.1% strikeout rate and velocity that didn’t line up with what he’d shown previously in Japan. The 2022 season brought some signs of encouragement, as the southpaw’s average fastball jumped by a hefty 2.5 mph (from 92.6 mph to 95.1 mph). Kikuchi saw a 50% increase in his strikeout rate, climbing from that ugly 16.1% mark to an above-average 24.2%. But his walk rate also jumped to nearly 11%, and he ultimately posted a second straight ERA north of 5.00.

Starting in early 2021, Kikuchi’s results took a turn for the better. He maintained the prior season’s velocity spike and strikeout gains but did so while improving his command. For a stretch of 11 starts in the middle of the 2021 season’s first half, Kikuchi was one of the most effective pitchers in baseball: 69 2/3 innings, 2.33 ERA, 27.5% strikeout rate, 8.3% walk rate, 58% ground-ball rate. Kikuchi was a deserving first-time All-Star and was pitching so well at the season’s midway point that I wrote about how he’d suddenly begun to make the question of whether to exercise a quartet of $16.5MM options one worth pondering. The extra four years and $66MM would’ve brought Seattle’s total commitment to the left-hander to seven years and $109MM in total.

Kikuchi wound up making it an easy call for the Mariners — though not in the way he and the team hoped. From July 5 through season’s end in 2021, the pendulum swung in the completely opposite direction for him. He was rocked for a 6.22 ERA as his walk rate spiked back over 10% and he became problematically homer-prone. Hackneyed as the line may be, 2021 was a true tale of two seasons for Kikuchi. A dominant, All-Star-caliber first half followed by a catastrophic second half in which he had the seventh-worst ERA of any pitcher with at least 60 innings pitched.

The Mariners unsurprisingly opted not to pick up their four-year, $66MM option on Kikuchi. While it originally looked as though Kikuchi would exercise his $13MM player option, he surprised some onlookers by instead declining that guaranteed sum and heading back to the market. There were plenty of critics at the time of his decision, but his eventual three-year, $36MM deal with the Blue Jays proved that he’d come out ahead on the gambit.

Kikuchi’s time in Toronto has been similar to his run with the Mariners. A disappointing first campaign saw him lose his rotation spot at one point and finish out the year with a 5.19 ERA in 100 2/3 innings. Heading into 2023, he wasn’t even guaranteed a spot in the rotation. And through his first 11 starts of the season, Kikuchi was again performing his typical highwire act. His 4.47 ERA was passable, but the lefty was averaging a staggering 2.4 homers per nine frames and showing a diminished 21.5% strikeout rate.

On June 4, something interesting happened. Kikuchi threw a curveball. It’s an unremarkable statement in and of itself, but it was the first time Kikuchi had thrown a hook since his rookie season in Seattle. Scouting reports on Kikuchi when he was headed stateside for the first time praised his curve as one of his top pitches, in fact. But major league hitters absolutely teed off against the pitch in 2019, posting an outrageous .353/.371/.632 slash against the suddenly ineffective curveball.

Kikuchi scrapped the pitch entirely for the 2020-22 seasons and hadn’t thrown it through 11 starts in ’23. For the remainder of the season, just under 13% of Kikuchi’s pitches were curveballs, per Sports Info Solutions. This, however, wasn’t the same curveball he showed in that rookie season. Kikuchi’s 2019 hook averaged just over 75 mph, featuring a huge 63.7 inches of vertical break and 6.9 inches of horizontal break, per Statcast.

The new breaker is a harder, sharper curveball that sits 83 mph with 43.5 inches of vertical break and 4.4 inches of horizontal break. The esteemed Rob Friedman — aka Pitching Ninja — has highlighted the offering on several occasions since last June. Compare that to this video of Kikuchi’s old curveball, and you can see it’s an entirely different pitch. The new curve wasn’t a dominant pitch last year — opponents hit .277/.306/.447 in plate appearances ending with a curveball — but the change in repertoire seemingly helped keep hitters off balance and make his other pitches more effective.

The 2024 season has been another story. Kikuchi has fully embraced the new curveball by throwing it at a 28% clip, and batters have been almost wholly unable to do damage against the pitch. Opponents are hitting .258/.290/.318 in 69 plate appearances that have ended with a curve, and their only four extra-base hits have been doubles. Nearly 53% of batted curveballs against Kikuchi have been grounders. This has helped him tamp down his longstanding struggles against right-handed opponents, and Statcast lauds the curveball as a plus pitch, giving opponents an “expected” .221 batting average, .293 slugging percentage and .240 wOBA against the pitch.

The uptick in curveballs has led Kikuchi to use his slider and changeup at some of the lowest rates of his career. All three of his non-fastball pitches have flummoxed opponents this season. His heater is averaging a career-high 95.6 mph despite Kikuchi pitching in his age-33 season, but it remains hittable and has been his weakest pitches in terms of opponent results. However, the incorporation of an effective curveball also makes it harder for opponents to sit on the heater.

Through 11 starts this season, Kikuchi has posted a 3.25 ERA. He’s totaled 61 innings, fanned 24.1% of opponents against an outstanding 5.1% walk rate and kept the ball on the ground at a solid 44.1% clip. Kikuchi is still giving up a fair bit of hard contact (mostly on that heater) and will surely see his tiny 7.7% homer-to-flyball ratio trend tick upward. League average tends to be in the 12-13% range, and Kikuchi’s career mark is 17.4%. Even with a couple extra homers on his 2024 ledger, however, Kikuchi would look like a clearly above-average starter.

And it’s not just the 2024 season where he’s been effective with this new offering. It’s now been almost one year to the day since Kikuchi broke out the new curveball, and his numbers over the past calendar year could catch some onlookers by surprise. His 3.45 ERA ranks 12th among 78 qualified starting pitchers, and he’s 28th in total innings (172 1/3). By measure of FanGraphs’ version of WAR, which is calculated off his 3.09 FIP rather than his raw run-prevention numbers, Kikuchi has been baseball’s fifth-most valuable pitcher. RA9-WAR, which is simply based on the number of runs he’s allowed (rather than FIP) has Kikuchi tied for 18th.

Regardless of one’s preferred method of pitcher evaluation, Kikuchi has been one MLB’s 10 to 20 best starters over the past calendar year — a remarkable turnaround for someone who entered the 2023 campaign fighting for a rotation spot with the team whose rotation he’s now anchoring.

Kikuchi’s gains are all the more interesting in light of the Blue Jays’ disappointing 2024 campaign. Toronto currently sits at 26729 on the season, placing them last place in the hyper-competitive AL East. They’ve rattled off four straight wins but are still 11.5 games out of first place in the division and 4.5 games out of a Wild Card spot (with three teams standing between Toronto and the third spot, currently held by the Twins). The Blue Jays’ playoff odds are hardly shot, but they’ve undeniably diminished relative to their preseason projections. There’s already speculation about the potential of a sell-off, with names like Bo Bichette and Vladimir Guerrero Jr. the subject of particular wishcasting.

But if the Jays do end up selling, it’s Kikuchi — not Bichette, Guerrero, Chris Bassitt, etc. — who stands as Toronto’s likeliest trade commodity. He’s playing out the final season of that three-year, $36MM deal and earning what now looks like a highly reasonable $12MM salary. The majority of contending clubs should be able to absorb some or all of the remaining salary on his deal, although the Jays could always offer to pay it down in order to sweeten a return. Kikuchi has pitched himself into qualifying offer candidacy, so the Jays would likely need some real prospect value to come their way in order to make the trade, but so long as he continues pitching close to his pace over the past 365 days, that’d also be a reasonable ask.

Further, Kikuchi’s status as an impending free agent makes his past calendar year all the more intriguing. If he can make another 20 or so starts at this pace, he’ll hit the market on the back of an impressive run and be able to stake his claim as one of the better mid-tier starters on the market. He’s not going to elevate himself into the Corbin Burnes or Max Fried tiers of the upcoming free-agent market, but another lucrative three-year deal would be in play. Both Bassitt and Sonny Gray scored three-year pacts at annual rates higher than $20MM covering the same age-34 to age-36 seasons Kikuchi will be peddling.

Kikuchi has a ways to go before he’s squarely in that conversation, his turnaround over the past year has him heading in that direction. It’s worth pointing out that he lasted only three innings during his last start, showing reduced velocity and failing to record a strikeout. That could be a red flag, but it could also just be a blip on the radar. The Jays haven’t pointed to any kind of medical issue for Kikuchi. We don’t know if there’s an injury, illness, pitch tipping or simple fatigue at hand, or whether it was just off day for the lefty.

What we do know is that over the past year, very few pitchers have been more successful and more valuable than Kikuchi. Adding a new pitch isn’t always a ticket to greener pastures, but it certainly has been for Kikuchi, who’s shaping up to be a potential impact deadline arm and a much more appealing free agent than anyone could’ve reasonably expected a year ago.

Photo courtesy of USA Today Sports Images