Why is Roki Sasaki such a big deal? Let’s dive in

It’s Roki Sasaki season.

Since news broke that the 23-year-old Japanese phenom is jumping stateside this winter, Sasaki has captured headlines and imaginations across the baseball world. A potential ace available for a relative pittance, the long-limbed hurler is firmly on the radar and within the budgets of all 30 teams.

Only time will unravel the mysteries of Sasaki’s incredibly complex free agency, so let’s spend some time investigating him as a player.

What type of pitcher is he exactly? What pitches does Sasaki throw? How hard are they? Does he come with injury or durability concerns? Who are some loose comparisons already in MLB? What are reasonable expectations?

Let’s dive into the data and build a big-picture scouting report on this offseason’s most sought-after arm.

Sasaki's first tastes of pro baseball

Sasaki has been a known commodity since his amateur days, when he threw a fastball 101 mph, breaking Shohei Ohtani’s record for the hardest fastball ever thrown by a Japanese high schooler. Despite drawing interest from MLB teams out of high school, Sasaki opted to play in NPB for the Chiba Lotte Marines, who drafted him first overall in 2019.

The highly touted hurler sat out the 2020 season to rest his young arm, at his team’s behest. In 2021, he broke out as one of the best pitchers in Japan’s top league. The next season, Sasaki solidified himself as a game-changing force, tossing a perfect game and, at one point, retiring 52 consecutive batters. Then he turned 21 years old. He pitched twice for Japan in the 2023 World Baseball Classic, starting the team’s semifinal game against Mexico, in which he dominated for 3 2/3 innings before a few soft knocks and a three-run blast sullied his line.

Back in NPB, Sasaki continued his excellence in 2023 and 2024 but struggled to stay healthy, hucking 202 innings combined across the two seasons.

Sasaki’s 2024

Although Sasaki logged 111 innings this past season and pitched to a 2.35 ERA, his stuff was unavoidably down. Most notably, his fastball clocked in at 1.9 mph slower on average than in 2023. He also missed a batch of starts due to an unspecified arm issue, an ailment that almost certainly played a role in his diminished velocity. But Sasaki was nails when it mattered, tossing eight shutout frames in his last outing of the year, a masterful, nine-strikeout showing in the playoffs.

Durability and injury concerns

If Sasaki were a “normal” free agent, one without a contract ceiling, there would be significantly more debate and conversation about his lack of durability. Across four seasons in NPB, he averaged less than 100 innings per season. In today’s game, with starting pitchers carrying fewer innings than ever before, that lack of bulk isn’t an issue, per se. But it’s worth noting that Sasaki has not shouldered the load expected of a traditional ace.

Unfortunately, an arm surgery, be it elbow or shoulder, seems inevitable for Sasaki. Essentially every MLB starter who throws this hard, except for 2024 NL ROY Paul Skenes, has gone under the knife at some point. Pitcher injuries are baked into the math today; whichever team signs Sasaki understands that reality. But because he’s going to be a bargain, his durability won’t be scrutinized as much as, say, Yoshinobu Yamamoto’s was a year ago.

Sasaki's arsenal

Sasaki throws three pitches: a four-seam fastball, a splitter and a slider. He used to throw a curveball but abandoned the offering in recent seasons.

In 2024, Sasaki threw the heater just under half the time, the splitter around 28% and the slider 25%. That represented by far the highest slider usage of his NPB career. During his dominant 2022, Sasaki was fastball/splitter about 90% of the time. Once he comes stateside, the slider projects to become an even more important weapon against right-handed hitters. Still, there are precious few big-league pitchers who throw a splitter this frequently.

The fastball

Despite the recent dip in velocity, Sasaki still throws outrageously hard for a starter. His “diminished” 96.9 mph average would've tied for seventh among MLB starters this past season. His 2023 average of 98.8 mph would've been just behind Skenes’ 98.9.

The uniqueness of Sasaki’s fastball is more than just pure heat. His heater boasts an extraordinarily rare combo of horizontal and vertical movement. In other words, Sasaki’s fastball stays “on plane” and darts in toward right-handed hitters.

A few reasonable comparisons currently in MLB are Skenes, Hunter Greene, Spencer Arrighetti and Jeff Hoffman. Skenes is the only current big-league starter whose velocity compares to peak, pre-2024 Sasaki. The Pirates rookie also has tons of horizontal movement but doesn’t quite have the same carry as Sasaki. Greene has the carry and the velocity, but less horizontal zip. Arrighetti has the shape but is in a lower velocity bracket. Hoffman is a reliever, but his heater shows a similar, though less impressive, shape to Sasaki’s.

This is all to say: If Sasaki’s heater never returns to pre-2024 levels, it's still a freakish pitch. If he starts hitting 99 again … it’ll be Skenes-ian and beyond.

The splitter

If Sasaki’s fastball is a unicorn, his splitter is a unicorn that breathes fire, speaks five languages and cooks a world-class risotto. There’s truly nothing like it.

Most splitters move down and toward the pitcher’s arm-side. The average right-handed MLB split this season was thrown at 86.5 mph and had 10 inches of horizontal break. Taijuan Walker’s splitter is a solid example of what the pitch typically looks like.

According to data presented by Marquee Sports’ Lance Brozdowski, Sasaki’s splitter averaged just 3.1 inches of horizontal break in 2023 and 0.6 inches in 2024. In other words, the pitch typically moves straight down. Watching video of Sasaki’s performance against Mexico in the WBC, I noticed that he seems to vary the shape of the splitter depending on the handedness of the hitter he’s facing. Against lefties, the pitch showed more pure downward break with a smidge of armside run, while against righties, the pitch featured a noticeable amount of cut.

Here’s a splitter to LHH Alex Verdugo:

Here’s a splitter to RHH Randy Arozarena:

It is, quite simply, one of the most unique pitches in the world, and it will be a burden for big-league hitters.

The slider

Sasaki’s slider is, all things considered, his least refined offering. He threw the pitch significantly more in 2024 and will likely continue that usage pattern once he gets to MLB. One would expect Sasaki to use the pitch almost exclusively against right-handed hitters as an offering that moves away from same-sided opponents. It’s a good pitch but one that will need to become more consistent.

Here's the rub on Roki

Sasaki is a monster talent, one who could soon develop into a soul-snatching, Cy Young-level pitcher. He offers a rare combination of current ability and upside. The only real total package comparison is Skenes, who debuted in MLB this past season and was almost immediately one of the best pitchers in the league (Skenes was recently announced as an NL Cy Young finalist).

The secondary metrics on Sasaki’s fastball are superior to Skenes', though Skenes is a much more physical presence. There will be bumps and significant injuries ahead for Sasaki — that’s just life as a pitcher — but there’s no question that the data back up the hype.