It’s Roki Sasaki season.
Since news broke that the 23-year-old Japanese phenom is jumping to the United States this winter, Sasaki has captured headlines and the imagination of the baseball world. The long-limbed pitcher is a potential top prospect available for a relatively small fee and 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 examining him as a player.
What type of pitcher is he exactly? What throws does Sasaki throw? How difficult are they? Are there any concerns about injury or durability? Who are there already loose comparisons in the MLB? What are reasonable expectations?
Let’s dive into the data and put together a comprehensive scouting report on this offseason’s most sought-after trade.
Sasaki’s first taste of professional baseball
Sasaki has been a known commodity since his amateur days, when he threw a 100 mph fastball, breaking Shohei Ohtani’s record for the hardest fastball ever by a Japanese high school student. Despite attracting interest from MLB teams since high school, Sasaki opted to play in NPB for the Chiba Lotte Marines, who drafted him first overall in 2019.
The highly touted pitcher rested his young arm for the 2020 season at the insistence of his team. In 2021, he broke out as one of the best pitchers in Japan’s top flight. The following season, Sasaki cemented himself as a game-changing force, pitching a perfect game and at one point retiring 52 consecutive batters. Then he turned 21 years old. He pitched twice for Japan in the World Baseball Classic and started the team’s semifinal against Mexico, dominating 3 2/3 innings before a pair of soft hits and a three-run explosion tarnished his line.
Back in NPB, Sasaki continued his stellar performances in 2023 and 2024, but struggled to stay healthy, throwing a combined 202 innings in the two seasons.
Sasakis 2024
Although Sasaki logged 111 innings last season and pitched a 2.35 ERA, his performance was inevitably low. Most notably, his fastball averaged 1.9 mph slower than it did in 2023. He also missed a number of starts with an unspecified arm problem, a condition that almost certainly played a role in his reduced velocity. But Sasaki was nails when it mattered, throwing eight shutout frames in his final outing of the year, a masterful nine strikeout that was on display in the playoffs.
Durability and injury issues
If Sasaki were a “normal” free agent, one without a contract cap, there would be significantly more debate and conversation about his lack of durability. Over four seasons in NPB, he averaged less than 100 innings per season. In today’s game, where starting pitchers have fewer innings under their belts than ever before, that lack of volume in itself isn’t a problem. But it’s worth noting that Sasaki hasn’t yet shouldered the burden expected of a traditional ace.
Unfortunately, arm surgery, whether for an elbow or a shoulder, seems inevitable for Sasaki. Essentially every MLB starter who throws that hard, save for 2024 NL ROY favorite Paul Skenes, has gone under the knife at some point. Pitcher injuries are baked into the math at this point; whichever team signs Sasaki understands that reality. But because he will be a bargain, his durability won’t be scrutinized as much as, say, Yoshinobu Yamamoto was a year ago.
Sasaki’s arsenal
Sasaki throws three pitches: a four-seam fastball, a splitter and a slider. He always threw a curveball, but dropped the offer in recent seasons.
In 2024, Sasaki threw the heater a little less than half the time, the splitter at around 28 percent and the slider at 25 percent. That represented by far the highest slider usage of his NPB career. During his dominant 2022, Sasaki was a fastball/splitter about 90% of the time. Once it comes to the United States, the slider threatens to become an even more important weapon against right-handed hitters. Yet there are very few big league pitchers who throw their splitter at this frequency.
The fastball
Despite the recent dip in velocity, Sasaki is still throwing insanely hard as a starter. His “reduced” average of 96.9 mph would have ranked seventh among MLB starters this past season. His 2023 average of 98.8 would have been just behind Skenes’ 98.9.
The uniqueness of Sasaki’s fastball is more than just pure heat. Its heater features an extremely rare combination of horizontal and vertical movement. In other words, Sasaki’s fastball stays “on plan” and shoots toward right-handed hitters.
Some reasonable comparisons currently in the MLB are Skenes, Hunter Greene, Spencer Arrighetti and Jeff Hoffman. Skenes is the only current big league starter whose speed is comparable to that of pre-2024 peak Sasaki. The Pirates rookie also has a lot of horizontal freedom of movement, but doesn’t quite have the same carry as Sasaki. Greene has the carry and the speed, but less horizontally. Arrighetti has the shape, but is in a lower speed class. Hoffman is a reliever, but his heater shows similar, if less impressive, form to Sasaki’s.
This is just to say, if Sasaki’s heating never returns to pre-2024 levels, it’s still an erratic tone. If he goes back to 99… it will 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 really is nothing like it.
Most splitters move down and toward the thrower’s arm side. The average right-handed MLB split this season was thrown at 80.5 miles per hour and had a horizontal break of 10 inches. Taijuan Walker’s splitter is a good example of what the field usually looks like.
According to data from Lance Brozdowski of Marquee Sports, Sasaki’s splitter averaged just 3 inches of horizontal break in 2023 and just 0.6 inches in 2024. In other words, the field generally moves straight down. While watching a 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 skill of the hitter he is facing. Against lefties the pitch showed a more pure downward break with a hint of armside run, while against righties the pitch showed a noticeable amount of cut.
Here’s a splitter for LHH Alex Verdugo:
Here’s a splitter for RHH Randy Arozarena:
It is simply one of the most unique fields in the world and will be a burden for major league players.
The slider
Sasaki’s slider is, all things considered, his least refined offering. He threw significantly more on the field in 2024 and will likely continue that usage pattern once he reaches the MLB. You would expect Sasaki to use the pitch almost exclusively against right-handed hitters as an offering moving away from same-sided opponents. It’s a good pitch, but it needs to be more consistent.
Here’s the problem with Roki
Sasaki is a monster talent, someone who could quickly develop into a true Cy Young-level pitcher. He offers a rare combination of current power and upside. The only true total package comparison is Skenes, who made his MLB debut 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 stats on Sasaki’s fastball are superior to Skenes’, although 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 doubt the data backs up the hype.
