Roki Sasaki and Major League Baseball: How effective would his pitching arsenal be?

Roki Sasaki is a stud dog. Probably.

He first caught the attention of the United States during the 2023 World Baseball Classic, when he hit 100 miles per hour on the fastball and announced his presence with authority. But the 23-year-old Sasaki has put up some crazy numbers in Japan, with a career 2.02 ERA, and there’s a chance he could come to Major League Baseball via the postal process this offseason. Everyone should be interested, and only a few will have the international money to step up to the table – the Chiba Lotte Marines could hold on to him for another two years, and players under 25 are subject to international bonus pool rules – but that doesn’t mean we knows everything there is to know about Sasaki as a pitcher.

To some extent, there is always a balance between what a team knows and what it doesn’t know about a free agent. Even with a mid-career player who has played Major League Baseball his entire professional career, there are things the acquiring team cannot know. Therefore it is probably true teams get more production when they re-sign their own players than when they take a player from another team. The assumption is that they know more about the player they already had, things like makeup and health.

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When you sign a pitcher from another league, the balance shifts to the unknown. Not only do they play in a completely different league, but they are also pitchers, and pitchers are subject to more seasonal swings in production. Pitching prospects still finish with worse results than pitching prospects, and even a pitcher as exciting as Sasaki is closer to a prospect than an established Major League pitcher.

That said, Sasaki has thrown in front of pitch-tracking machines, played at some of the highest levels of baseball outside of the major leagues, and given us some insight into where he stands health-wise. We can follow the breadcrumb trail to get an idea of ​​how teams might feel about him during a potential postseason. His availability isn’t set in stone, but perhaps we can understand his talent if we use the modern tools of pitching analysis.

The stuff

Sasaki pitched at the 2023 World Baseball Classic, giving us pitch motions and velocities that can help us put the physical characteristics of his pitches on par with MLB pitchers. There he had an excellent 111 Things+ overall, which ranked him among the top 10 starters at that tournament and would have placed him among the top 10 qualified starters in the big league this past 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 wanted to be there. They threw harder fastballs in shorter outings. The average starter who pitched in the WBC and then again in the big league over the past two years lost about five points to Stuff+ in the transition. Someone like Shota Imanaga, who had a great season with the Chicago Cubs, lost even more because he was used as a reliever. Sasaki averaged 100 mph on his fastball with great biplane movement, and by Stuff+ he had the best fastball among the starters not named Shohei Ohtani in that tournament.

He’s already lost some of that speed in Japan, averaging 98.9 mph in 2023 and then 96.9 this past season. That speed is probably quite important. Sasaki had over 17 inches of induced vertical movement and 13 inches of horizontal movement in the WBC. At over 60 miles per hour, his fastball compositions for those numbers include hard-throwing relievers like Kansas City Royals closer Lucas Erceg and New York Mets setup man Ryne Stanek, and perhaps Hunter Greene as a starter. Among 96-plus players, the compositions are a little less exciting: Cleveland Guardians starter Gavin Williams and reliever Yimi García have some similarities with their fastballs. And, according to Lance BrozdowskiSasaki also lost an inch of ride on the fastball in Japan in 2024. Regardless, it’s a very good fastball, but there are some indications that it’s going in the wrong direction.

His slider was a gyro slider with a speed of 140 km per hour, meaning it is a ball slider without much movement. That WBC slider would pair well with sliders thrown by Seattle Mariners closer Andrés Muñoz and Pittsburgh Pirates starter Mitch Keller. However, this past season it had dropped to 83.6 mph, and that’s below the 80 mph threshold for great gyro sliders, and now it looks more like Royals starter Brady Singer’s slider. Still an asset, but you may be sensing a theme here.

Splitters are difficult to handle in small samples, but according to this NPB pitch profilerSasaki’s splitter got a whiff a whopping 57 percent of the time batters swung last year (25 percent of all pitches). Only the Cincinnati Reds’ Fernando Cruz had a better whiff rate in the MLB this year, and Imanaga was extremely dependent on his splitter last season with a 42.9 percent whiff rate.

Sasaki’s splitter passes the eye test:

Roki Sasaki’s splitter from an NPB match early last season. This one was going 90mph, and you can see the wide four-seam grip in the close-up. It kills a remarkable amount of spin because of how fast the pitch is. pic.twitter.com/u9fqQBqZTr

— Lucas (@DBITLefty) March 20, 2023

It’s top-shelf material from Sasaki, on par with any pitcher that has come over from Japan, even if a little less so.

The results

Two years ago, Sasaki had a season for the ages. In 2022, he had a 2.02 ERA with 173 strikeouts against just 23 walks in 129 1/3 innings. Just unscrupulous. He followed that up with a season that was even better in rates and strikeouts (1.78 ERA, 135 strikeouts), but shorter in innings (91) due to an oblique injury. This year, bouts of upper-body fatigue and sore arms held him to 111 innings with a 2.35 ERA, but a reduced K rate: just 129 strikeouts. This follows the trend established above, where he had obscene things at age 20 in Japan, and then started to fall off that peak to some extent.

But if you use three-year figures to capture both the peak and what came after, it profiles itself very well as an important statistic. Because NPB doesn’t have that many power hitters, it’s difficult to convey things like ERA or home run rate. For example, Yoshinobu Yamamoto gave up two (two!!) home runs in 171 innings in Japan in 2023 before coming over and giving up seven in 90 innings against Major League players this year.

If we use strikeouts minus walks instead, we have a statistic that has done a good job of predicting the success of pitchers coming over from Japan. Nine pitchers have moved on to start at least 15 games in the MLB and had a strikeout-minus-walk rate of at least 18 percent in the three NPB seasons prior to their move. There are only two pitchers on the list who count as disappointments. Nine pitchers also transferred with a strikeout-minus-walk rate of less than 18 percent and started more than 15 games in the MLB. Hideo Nomo, Yusei Kikuchi, Hisashi Iwakuma and Kenta Maeda are the success stories on that list.

Look where Sasaki sits among his peers.

But again, Sasaki fell off. He had a strikeout-minus-walk rate above 30 percent for two years, and last year that dropped to 21.6 percent. Of course, you may be concerned about declining business and results. But that 21.6 percent figure would have ranked fifth on this list, between Masahiro Tanaka and Imanaga. Still pretty good.

The eye of the beholder will have a major say in the negotiations. Either Sasaki is an oft-injured pitcher with already declining qualities, or he has some of the best quality we’ve ever seen from a pitcher coming along. even afterwards that decay. Given the nature of the contract negotiations, a team that convinces Sasaki that they can help him return to 2022 in terms of health and such could be the team that seals the deal.

(Photo of Roki Sasaki pitching in the World Baseball Classic on March 20, 2023: Eric Espada / Getty Images)