By Eno Sarris / The Athletic
Roki Sasaki is a star. Probably.
He first attracted stateside attention in the 2023 World Baseball Classic with his 100-mph fastball and authoritative mound presence. And Sasaki, 23, has been putting up some huge numbers in Japan, with a 2.02 career earned run average.
The Chiba Lotte Marines, Sasaki’s club in Nippon Professional Baseball, announced early Saturday that they will post the right-hander, thus making him available to MLB teams in what is expected to be a wide-open sweepstakes for his services. Once Sasaki is posted, he has 45 days to sign.
Every team should be interested in Sasaki. But we don’t know everything there is to know about him as a pitcher.
To some extent, there is always a balance between what a team knows and doesn’t know about a free agent. Even with a midcareer position player who has played in MLB for his entire career, there are things the acquiring team can’t know. That’s why it’s probably true that teams get more production when they re-sign their own players than when they poach a player from another team. The assumption is that they know more about things like a player’s makeup and health if he has already played for them.
When signing a pitcher from another country that balance is skewed toward the unknown. Not only have they been facing a different caliber of competition, but as pitchers they are subject to more season-to-season swings in production. Pitching prospects still end up with worse outcomes than hitting prospects, and even a pitcher as exciting as Sasaki is closer to being a prospect than an established major league pitcher.
That said, Sasaki has pitched in front of pitch-tracking machines, has played at one of the highest levels in baseball outside of the big leagues, and has given us some insight into where he stands healthwise. We can follow the crumb trail to get a sense of how teams might be thinking of him during a possible posting period. His availability is not etched in stone, but maybe we can understand his talent if we use the modern tools of pitching analysis.
The stuff
Sasaki pitched at the World Baseball Classic in 2023, giving us movement and velocity information that can help us put the physical characteristics of his pitches on the same footing as pitchers from MLB. There, he had an excellent overall rating in Stuff+, a metric that looks only at the physical characteristics of a pitch, which had him in the Top 10 among starters at that tournament and would have put him in the Top 10 among qualified big league starters last season. He was behind Cristian Javier and Sandy Alcantara at the WBC, but ahead of Jesús Luzardo and Pablo López.
One thing we know about that tournament is that the players were amped to be there. They threw harder fastballs in shorter outings. The average starter who pitched in the WBC and then again in the big leagues over the past two years lost about five points of Stuff+ in the transition. Someone like Shota Imanaga, who had a great season for the Chicago Cubs, lost even more because he was used as a reliever.
Sasaki averaged 100 mph on his fastball with great two-plane movement and, by Stuff+, he had the best fastball among starters not named Shohei Ohtani in that tournament. He has lost some of that velocity already in Japan, averaging 98.9 mph in 2023 and then 96.9 last season. That velocity is probably pretty important. Sasaki had 17-plus inches of induced vertical movement and 13 inches of horizontal movement in the WBC.
At 98-plus mph, his fastball compares to relievers like Kansas City Royals closer Lucas Erceg and the New York Mets setup man Ryne Stanek, and maybe to Hunter Greene among starters. At 96-plus, the comps are a little less exciting: Cleveland Guardians starter Gavin Williams and reliever Yimi García have some commonalities with their fastballs. And, according to analyst Lance Brozdowski, Sasaki also lost a couple of inches of ride on the fastball in 2024 in Japan. It’s a really good fastball either way, but there are some indications that it’s moving in the wrong direction.
His slider was an 87 mph gyro slider, meaning it’s a bullet slider without a lot of movement. That WBC slider would compare well to sliders thrown by Seattle Mariners closer Andrés Muñoz and Pittsburgh Pirates starter Mitch Keller. It was down to 83.6 mph last season, though, and that’s below the 85-mph threshold for great gyro sliders, and now it looks more like the slider of Royals starter Brady Singer. Still an asset, but you may sense a theme here.
Splitters are hard to get a handle on in small samples, but according to a pitch profiler, Sasaki’s splitter got a whiff a whopping 57% of the time batters swung last year (25% of all pitches). Only Cincinnati Reds reliever Fernando Cruz this year had a better whiff percentage in MLB, and Imanaga ended up depending immensely on his splitter, with a 42.9% whiff rate last season.
It’s top-shelf stuff from Sasaki, on par with any pitcher who has come over from Japan, even if it’s down a little.
The results
Two years ago, Sasaki had a season for the ages. In 2022, he sported a 2.02 ERA with 173 strikeouts against only 23 walks in 129 1/3 innings. He followed that up with a season that was even better by rates and strikeouts (1.78 ERA, 135 strikeouts), but shorter on innings (91) because of an oblique injury. Last season, bouts of upper-body fatigue and arm soreness held him to 111 innings with a 2.35 ERA but a reduced K rate — only 129 strikeouts. This follows the trend, where he just had great stuff at age 20 in Japan, and then started to fall off that peak to some degree.
Still, if you use three-year numbers to capture both the peak and what came after, he profiles well in a key statistic. Because Nippon Professional Baseball doesn’t have as many power hitters, it’s tough to compare things like ERA or home run rate. For example, Yoshinobu Yamamoto gave up two homers in 171 innings in Japan in 2023 before coming over and giving up seven in 90 innings against major leaguers this year.
Sasaki has fallen off some. He had a strikeout-minus-walk rate above 30% for two years, and then last year it fell to 21.6%.
The eye of the beholder will have an outsize say in the negotiations. Either Sasaki is an oft-injured pitcher with already declining stuff, or he’s got some of the best stuff we’ve seen from a pitcher coming over even after that decline.
Given the nature of contract negotiations, a team that persuades Sasaki that it can help him get back to 2022 in terms of health and stuff might be the one that seals the deal.
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