Rōki Sasaki is coming to MLB: How good is he and where will he sign?

The MLB offseason kicked off with some seismic news. Japanese phenom Rōki Sasaki is going to be posted by his former team, the Chiba Lotte Mariners of Nippon Professional Baseball. That means the 23-year-old, who is a two-time NPB All-Star and holds the NPB record with 19 strikeouts in a single game, will be eligible to sign with any team in the offseason.

While many people are just going to assume that Sasaki will sign with the Dodgers, there are a lot of moving pieces here due to Sasaki’s age and the time of year that he becomes a free agent. This article will attempt to clear all of that up in addition to explaining just who Rōki Sasaki is and how good we can expect him to be when he arrives stateside.

For this article, I’ll be referencing two key sources. Eno Sarris wrote a great article on The Athletic breaking down Sasaki’s pitch mix, and Lance Brozdowski also posted a video analyzing the shape/movement of his pitches based on NPB data. Those are both absolutely worth checking out if you want even more detail than I can give you here.

Who is Rōki Sasaki?

Sasaki is a 23-year-old right-handed pitcher (he just had his birthday on November 3rd) who is among the most heralded pitchers in Japanese history. He threw 101 mph while in high school, which set a Japanese record, and was the most sought-after prospect in years. He spurned MLB teams in 2019 and entered the NPB Draft, where the Mariners took him first overall. COVID delayed his NPB debut, but he pitched to a 1.84 ERA with 87 strikeouts in 83.1 innings as a 19-year-old in 2021.

In 2022, he posted a 2.02 ERA with 173 strikeouts to only 23 walks in 129 1/3 innings and then followed that up with a 1.78 ERA and 135 strikeouts in only 91 innings in 2022 due to an oblique injury. This year, he posed a 2.35 ERA but had a few issues with upper-body fatigue which limited him to 129 strikeouts in 111 innings.

Over his four years, that has given him a 2.02 ERA, 0.88 WHIP, and 524 strikeouts to 91 walks in 414.2 innings. Those are insane numbers for a pitcher who is so young, but there are obvious concerns that he has had two seasons cut short by injuries so far. At 6’4″ and 205 pounds, he has the frame to hold up to a larger workload and has elite athleticism, so there shouldn’t be too many concerns about his durability. Tom Verducci of Sports Illustrated compared Sasaki’s mechanics to Zack Wheeler, which is intriguing because Wheelers also dealt with injuries early in his career before emerging as a workhorse.

So either Sasaki is a phenom who will consistently battle injuries that could limit him from reaching his ceiling or he has the upside to be one of the best pitchers in baseball and is only 23 years old. The upside feels worth the gamble for any MLB team.

What pitches does Rōki Sasaki throw and will they translate against MLB hitters?

According to Eno Sarris, at the 2023 World Baseball Classic, Sasaki posted an overall Stuff+ number of 111, which made him a top 10 starter in that tournament and would have made him a top 10 starter in MLB in 2024. So how does his arsenal get him there?

Well, it starts with the fastball that touched 101 mph when he was in high school. He sat around 99 with 18 inches of vertical break in 2023. When compared to the average MLB four-seamer, it was an elite pitch (data courtesy of Lance Brozdowski’s video).

The two issues with Sasaki’s fastball are that the NPB ball is stickier so that often leads to more movement, and Sasaki also saw a dip in both movement and velocity in 2024 as he dealt with arm fatigue. That dip is a significant one, as Eno Sarris put it: “At 98-plus mph, his fastball comps to those numbers are hard-throwing relievers like Kansas City Royals closer Lucas Erceg… and maybe Hunter Greene among starters.” But Sasaki averaged just 96.9 this past season and also lost a couple of inches of ride on the fastball.

It’s still a plus pitch, but we have to hope the 2024 regression, and the MLB baseball, won’t impact it too much. Lance Brozdowski suggested in his video that much of Sasaki’s fastball regression in 2024 could have been linked to mechanical changes that people picked up on as Sasaki compensated for arm fatigue. If Sasaki’s decline in fastball shape and velocity was really a mechanical issue, then his signing with a team that has a strong track record of developing pitching could lead to him regaining some of the lost velocity and shape and featuring one of the best fastballs in baseball.

Sasaki pairs his fastball with an 87 mph gyro slider, meaning it’s a bullet slider without a lot of movement. According to Eno Sarris, the slider Sasaki showcased in the World Baseball Classic “comp well to sliders thrown by Seattle Mariners closer Andrés Muñoz and Pittsburgh Pirates starter Mitch Keller. It was down to 83.6 mph this past season, though, and that’s below the 85 mph threshold for great gyro sliders, and now it looks more like Royals starter Brady Singer’s slider.”

Again, another pitch that was impacted by his arm fatigue but one that flashed plus characteristics in years past.

The bullet shape of the slider is similar to the bullet shape of the splitter, which is odd for a splitter. Sasaki’s splitter doesn’t move arm side much at all. It almost seems to knuckle and drop as it approaches the plate. As Lance Brozdowski mentioned, it’s hard to compare it to another splitter because there aren’t many splitters in baseball that have so little arm-side movement. Yet, the splitter has been an elite pitch for Sasaki, so it seems to work.

As Eno Sarris mentioned, “According to this NPB pitch profiler, Sasaki’s splitter got a whiff a whopping 57 percent of the time batters swung last year (25 percent of all pitches).” We saw Shota Imanaga come over from Japan and depend on his splitter a lot, throwing it 31% of the time and getting a 43% whiff rate this past season, so Sasaki could use the splitter similarly in 2025.

Eno Sarris’ article also had a useful chart using K-BB% from NPB data to show how other Japanese pitchers who came over have fared. Since his article is behind a paywall, I don’t want to give out that full data but Sasaki’s 28.4% K-BB% over the last three seasons is 6% better than Shohei Ohtani, Yu Darvish, and Yoshinobu Yamamoto when they came over. Since Ohtani has posted a 3.01 MLB ERA and Yu Darvish has a 3.58 MLB ERA, it seems fitting to assume that Sasaki can post a low 3.00 ERA when he comes stateside.

Projections for Rōki Sasaki

Given all the information I cited above, I think Sasaki saw a dip in performance due to upper body fatigue and the consequential mechanical issues that arose because of it. There are indications that he wants to sign with a team that has a track record of developing pitchers because he knows he has improvements to make – like a better strikeout pitch against righties. As a result, I do think some of the issues that many people are pointing out from 2024 as things that Sasaki can fix over time, and I would be easily taking him 1.1 in First Year Player Drafts and drafting him inside the top 50 overall in dynasty formats.

In redraft leagues. I feel comfortable predicting an ERA around 3.10 – 3.30 for Sasaki with something around a 28-29% strikeout rate. I think he will probably be limited to around 150 innings due to his prior workload and the team who signs him thinking about his development and not just 2025 results. Those results would have put him around Jack Flaherty’s performance this past season, and he finished as the 12th-ranked starting pitcher on the FanGraphs Player Rater.

What type of contract will Rōki Sasaki sign?

Because of his young age, Sasaki is not a traditional free agent like Yoshinobu Yamamoto was last year. According to Jeff Passan, the timing of Sasaki’s posting, which hasn’t been determined yet, will decide whether he enters the 2024 or 2025 international amateur class. If Sasaki is posted by Chiba soon and signs before December 15th, then he would count towards the 2024 international amateur class, and many teams have already used up almost all of their allotment on previous signings.

Given we are so close to the cut-off for the 2024 international period, it’s looking like Sasaki will count towards the 2025 international free agent pool and wait until January to be posted. That means teams can use their entire 2025 bonus pool to sign him if they want. Based on these international amateur class rules, Sasaki would also initially sign a minor league contract, and then the team that signs him could promote him to its major league roster before the 2025 season begins or they could choose to leave him in the minors for additional seasoning and development.

Related: 2024 MLB Free Agent Tracker

Who are the favorites to sign Rōki Sasaki?

The obvious frontrunner is the Dodgers given Sasaki’s relationship with Yamamoto and Ohtani, and the fact that they are currently the best team in baseball, coming off a convincing World Series win. However, since Sasaki can only accept international bonus slot money right now, the Dodgers can’t necessarily win his services based on money alone. The Athletic has reported that Sasaki will likely prioritize stability, lifestyle, comfort, and a team’s track record with player development. That may still favor the Dodgers, but it could open up opportunities for other teams.

If Sasaki does post in the 2025 international period then every team is free to sign him and some interesting teams will have the most money, which is $7,555,500. Some of those teams are Detroit, Minnesota, Oakland, Seattle, and Tampa Bay. Seattle has a track record with developing pitchers and continues to have a great relationship with Ichiro Suzuki. The Rays also have a long track record of developing pitching well, and Sasaki’s unique posting conditions would not force them to offer a lucrative contract.

If you go to the next level of the bonus pool, teams like Baltimore, Arizona, and Cleveland have $6,908,600 to spend, but they feel less likely in terms of pitcher development success, stability, and success with prior Japanese players. The level below that is $6,261,600, which includes Atlanta, Boston, Chicago Cubs, both New York teams, Philadelphia, San Diego, and Texas. There are a lot of contenders here. The Red Sox, Cubs, Mets, and Yankees all have the money and stability to offer Sasaki a place to spend his entire career. They have also all had previous success with Japanese players and are contenders or have been in the recent past. San Diego also has Yu Darvish, who has a personal connection with Sasaki, and they are a current contender as well.

The last bonus pool is $5,146,200 which includes the Dodgers and Giants. This means Sasaki would be forfeiting over $2 million in 2025 to sign with the Dodgers but that’s not a deal-breaking amount.

At the end of the day, the Dodgers are the favorite but I wouldn’t rule out the Padres, Red Sox, and Mets as real contenders, and the Mariners as well if they were to make a trade to free up a spot in their rotation.