In the semifinals of the 2023 World Baseball Classic, Team Japan faced Team Mexico, competing for a chance to play Team USA in the championship game. Starting on the mound for Japan was 21-year-old phenom Roki Sasaki, best known to American audiences for pitching a 19-strikeout perfect game in NPB during the 2022 season. With a four-seam fastball averaging 100.5 MPH and a devastating 91.2 MPH splitter, Sasaki struck out three batters over four innings, providing many observers with their first glimpse of his potential as a future front-of-the-rotation starting pitcher.
Fast forward to this past winter, and Sasaki became one of the most highly coveted international free agents available. After evaluating multiple offers, Sasaki ultimately signed with the Los Angeles Dodgers for a $6.5 million signing bonus. Despite entering the 2025 season amid lofty expectations, Sasaki encountered some setbacks during 2024, such as a regression in his fastball velocity and ongoing command issues, that have persisted into his early Major League career. This article will examine Sasaki’s pitch arsenal, attempt to identify the underlying causes of his current struggles, and seek to predict the adjustments he will make to his pitch arsenal to realize his top-of-the-rotation potential for the Los Angeles Dodgers.
Overview
As shown by the short-form movement plot above, Sasaki’s current arsenal features three pitches: a four-seam fastball, a splitter, and a slider. Throughout his professional career, Sasaki has utilized his four-seam fastball to overpower hitters with plus velocity, while using the slider to generate swing-and-miss against right-handed hitters and his splitter to generate swing-and-miss against hitters of the opposite handedness. Sasaki’s splitter is arguably the most unique pitch in all of Major League Baseball, generating nearly 5 inches of drop with little arm-side run at 85.1 MPH. Visually, the pitch looks like a deathball slider, however, Sasaki clearly throws the pitch with a split-finger grip, and he is able to kill a lot of spin off the pitch, with the offering averaging 511 RPM so far this season. The movement profile and sheer uniqueness of the offering are significant contributors to the 46.2% whiff rate the pitch has generated in 2025. Sasaki throws his four-seam fastball with plus velocity, averaging 97.0 MPH, while the pitch approaches “dead zone” shape with ~14 inches of induced vertical break and ~11 inches of arm-side run. Sasaki also possesses a slider with ~11 inches of horizontal movement at 83.1 MPH.
Pitch models vary in their evaluations of the quality of Sasaki’s pitch arsenal. Taking a look at four major pitch quality models (FanGraphs’s Stuff+, PLV, my aStuff+ model, and PitchingBot), each model agrees that Sasaki’s four-seamer and slider grade as below-average pitches, with PitchingBot being the only model that believes Sasaki’s four-seamer is at least league-average. Pitch quality models tend to have difficulty evaluating off-speed pitches, and Sasaki’s splitter is so unique that I’d imagine most models have a difficult time finding a similar pitch to compare the offering to. In my opinion, given the pitch’s unique movement profile at 85.1 MPH, I believe that PitchingBot most accurately grades the quality of this offering with a grade of 75.
As it pertains to locating his offerings, Sasaki has experienced some difficulties early in his Major League career, resulting in a 20.3% walk rate over his first 13.2 innings pitched. As shown by the location plots above, Sasaki has experienced some difficulties in locating his splitter, with the pitch being located all over the strike zone. Splitters can be difficult to command and locate, given the pitch’s awkward grip, and I would imagine that the nature of the pitch has a large effect on Sasaki’s difficulties in commanding the offering. Sasaki’s splitter has been compared to a knuckleball in terms of its movement profile, and I believe it is important to keep this comparison in mind when evaluating his ability to locate the pitch. Sasaki has demonstrated a better ability in locating his four-seamer, frequently utilizing the pitch down in the zone, a strategy the Dodgers seemingly like to utilize, while he has experienced difficulties locating his slider.
Disclaimer about Sasaki’s splitter control aside, I would grade Sasaki’s command as below-average, consistent with the 40/45 command grade that FanGraphs gave Sasaki before the 2025 season and the 83 Location+ grade he has generated so far this season. Addressing these command issues will be crucial in determining Sasaki’s future effectiveness as a top-of-the-rotation starting pitcher.
Potential Changes
The main question of this article is, what changes will Roki Sasaki make to his pitch arsenal over the course of the season to inch closer to his potential as a top-of-the-rotation starter for the Los Angeles Dodgers? I believe that the first change he will make will be to add a second fastball to his pitch arsenal. As mentioned earlier, despite possessing plus velocity on the offering, opposing hitters have been able to generate a lot of offensive production against Sasaki’s four-seamer this season, with a .414 xwOBA and 11.8% whiff rate against the pitch this season. This is likely because Sasaki’s four-seamer is considered to have “dead zone” shape.
Each pitcher creates an expectation of their movement profiles to the opposing hitter based on their average arm angle and release point. For example, if a pitcher throws over-the-top they are expected to have a north-south arsenal while if a pitcher throws sidearm they are expected to have an east-west arsenal. The expected movement profile for each pitch based on these factors is known as the “dead zone” (as visualized by Max Bay with his dynamic dead zone app), and hitters tend to generate a significant amount of offensive production against pitches with expected movement profiles.
There are three main methods by which a pitcher can take their fastball out of the “dead zone”. One method is that they can simply alter the movement profile of their primary fastball (Spencer Schwellenbach did this by adjusting his four-seam grip), however, this typically involves mechanical and/or grip adjustments that can be difficult to implement in reality. Another method is that the pitcher can simply throw a dead zone fastball at maximum velocity, which is how Paul Skenes’s fastball is still effective despite possessing dead zone shape. While this is a common fix for dead zone fastballs, Sasaki already averages ~97 MPH on his four-seamer and still struggling to generate good results with the offering.
A third method in which a pitcher can improve the performance of a dead zone fastball is to “mask” the pitch by adding multiple fastballs to their pitch arsenal. Utilizing multiple fastballs has become a prominent trend across Major League Baseball in recent seasons, as forcing opposing hitters to discern between multiple fastball shapes can induce hitters to generate weak contact, and can help a four-seamer with below-average shape “play up” and generate more whiffs due to the added deception in the pitcher’s arsenal. For these reasons, I believe that adding a cutter and/or sinker to his arsenal will be an important development for Sasaki’s pitch arsenal moving forward. Adding a sinker would allow Sasaki to generate sub-optimal contact against right-handed hitters, and more swing-and-miss on the four-seamer when hitters anticipate the wrong fastball shape. Adding a cutter would allow Sasaki to generate these results against left-handed hitters, and he could perhaps mix the offering in against right-handed hitters as well. The Dodgers added a sinker to Yoshinobu Yamamoto’s pitch arsenal last season to improve his fastball production, and I would expect the Dodgers to pursue the same path of development with Sasaki this season.
Another reason why Sasaki could benefit from adding an additional fastball to his pitch arsenal is that he has shown to be predictable, especially when he falls behind the count. The table above displays the usage rates of the pitches in Sasaki’s arsenal, grouped by batter handedness and count state. When Sasaki is behind in the count (2-0, 2-1, 3-0, 3-1), he leans heavily on his four-seamer, utilizing the offering 73.9% of the time to right-handed hitters and 89.7% of the time to left-handed hitters. This causes hitters to have a “flashing green light” to anticipate a four-seamer in the zone during these counts, leaving Sasaki extremely vulnerable to allowing hard contact. Tuning down the four-seam usage when he’s behind in the count and adding a cutter (to left-handed hitters) and/or a sinker (to right-handed hitters) will make it more difficult for opposing hitters to correctly anticipate Sasaki’s tendencies, as it opens up the possibility for hitters to guess the wrong fastball, resulting in off-barrel contact. In addition to adding a second fastball to his pitch arsenal, I also believe that Sasaki could increase his slider usage early in counts against left-handed hitters in an attempt to generate called strikes (this will require an improvement in his ability to command the offering), and he would likely benefit from improving his four-seam usage to left-handed hitters in two-strike counts to prevent hitters from easily anticipating his splitter. These adjustments to his pitch usage and arsenal composition would likely improve Sasaki’s overall effectiveness, and allow him to inch closer to his potential as a frontline starter.
Concluding Thoughts
While the beginning of his Major League career has certainly been filled with ups and downs, I am bullish on Sasaki’s ability to make adjustments and reclaim his top-of-the-rotation potential for the Los Angeles Dodgers. While I have certainly made the mistake of being impatient with the projections of young players in the past, it is important to note that Sasaki is only 23 years old, and with a pitch as uniquely dominant as his splitter and an ability to throw a fastball with above-average velocity, Sasaki clearly possesses a solid foundation for further development.
The Dodgers are one of, if not the best, organization in Major League Baseball as it pertains to pitching development, and whether they suggest he adds an additional fastball or new breaking ball to his pitch arsenal, I am confident that they will provide him with the best guidance on reaching his full potential. While the results have been underwhelming to start his Major League career, I believe that with the proper adjustments to his arsenal, Roki Sasaki will be a fixture in the Los Angeles Dodgers rotation for years to come.
Photo courtesy of Icon Sportswire | Adapted by Aaron Polcare (@abeardoesart on Bluesky and X)
