Roki Sasaki prospect profile: Japanese phenom has obvious holes in his game

Once Juan Soto was off the market, the Roki Sasaki sweepstakes immediately became the most enamoring story of the MLB offseason. The 23-year-old phenom will come to the MLB boasting an explosive fastball that tops 100 mph and a wipeout splitter that offsets his lightning heater. As an international amateur, his salary is capped to a minor-league salary, making him a legitimate target for essentially every MLB team.

Sasaki recently narrowed his list of preferred teams to three: the Toronto Blue Jays, Los Angeles Dodgers, and San Diego Padres. Among the top reasons he has chosen these teams as his top three would be their track records for pitching development. Sasaki dazzled on the mound for NPB’s Chiba Lotte Marines, pitching to a 2.35 ERA with 129 strikeouts through 111 innings. It was his highest ERA in his four seasons in the NPB. His career ERA stands at 2.02. But as astounding as his arm is, there may be some drawbacks.

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Breaking down Roki Sasaki's pitch arsenal

Among the top reasons Sasaki chose the three teams still on his list would be their track records for pitching development. The team that lands him will have a few flaws to hammer out.

For one, Sasaki has never pitched more than 129.1 innings in a single season. Enduring a full season’s workload isn’t something you can teach; only experience can do that. But let’s focus more so on things within the control of the manager and coaches. Sasaki’s 10.5 K/9 rate in 2024 is lower than in the past two years; down from 13.4 in 2023. His 2.6 BB/9 rate is the highest of his career; up from up from 1.7 in 2023.

And lastly, his H9 (hits per nine innings) in 2024 also stood at a career-high of 6.7; up from 5 in 2023. Several stats are trending in the wrong direction, so, let’s break it down pitch by pitch using the latest scouting report from MLB.com’s Jonathan Mayo.  

Sasaki’s key pitch is his fastball, but his average fastball velocity dropped from 98.8 mph in 2023 to 96.8 mph in 2024. A drop in velocity for a starter that throws 100+ mph isn’t as concerning since it reduces the risk of injury. And for a starter that hasn’t pitched 130 innings, this may be a good thing. What is concerning is that his arm side run has diminished, significantly decreasing the deception on his primary pitch. This might explain why Sasaki had less success missing bats in 2024.

In 2023, Sasaki’s fastball accounted for 24 percent whiff rate and 57.3 percent groundball rate. In 2024, this number shrunk to just 13.1 and 50 percent respectively. To better illustrate the difference, his fastball whiff rate went from elite to mildly below-average in just one year. For the pitching coach who gets the honor of coaching Sasaki, re-establishing his arm side run may be the top priority.  

One thing that isn’t a concern is Sasaki’s splitter. His splitter has improved since 2023 and has become the most devastating weapon in his arsenal. It accounted for a 57.1 whiff rate in 2024, which would place him second in the MLB to reliever Fernando Cruz. While we don’t know how his splitter will perform against batters in the MLB, in Japan, the splitter is a common pitch. Posting an elite whiff rate with a splitter in Japan may be an overwhelming x-factor Sasaki will bring to the MLB, where the pitch isn't as common.

Lastly, Sasaki will be packing a slider in his arsenal. Sasaki’s slider is said to be slightly above average to plus according to the scouting report. Still, Sasaki saw a decline in one important metric with this pitch. Sasaki’s slider was responsible for a 40.7 percent whiff rate in 2024. This was down from 48.6 percent in 2023. However, the groundball rate on his slider improved over that time from 42.9 percent to 53.6 percent.

For a starter who throws only three pitches, the effectiveness of his three-pitch mix will be key in determining his success on the MLB level. With this in mind, Sasaki’s slider will be a pitch his new team will want to work on.

But just in case, if he or his team his team chooses, it might be a good idea to develop a fourth pitch. Sasaki threw two curveballs in 2023. If he can develop that pitch at all, Sasaki could add another way to deceive hitters sitting on his off-speed slider/splitter combo.