After 4 starts, what can we make of Dodgers rookie Roki Sasaki?

On Saturday at Dodger Stadium, 23-year-old right-hander Roki Sasaki took the mound for the fourth start of his highly anticipated rookie season and delivered his best performance yet, allowing just one run over five innings of work. Unfortunately for his team, Sasaki’s strongest start to this point was also the first one to result in an L.A. loss.

The Dodgers won Sasaki’s first three starts despite his relative struggles, but they failed to provide him with any run support Saturday against the Cubs, and then the bullpen imploded entirely in the late innings, leading to a 16-0 rout in Chicago’s favor despite Sasaki’s stellar effort. As a result, Sasaki has his first loss and is still in search of his first win as a big-league starting pitcher.

While the unique circumstances of his jump to MLB mean that Sasaki is on the same league-minimum contract as fellow rookie hurlers Jack Dreyer and Ben Casparius, the immense hype surrounding his arrival has amplified the degree to which Sasaki’s earliest outings have been scrutinized. No, he didn’t require the same monumental monetary investment as his teammate Yoshinobu Yamamoto, but Sasaki’s development is being tracked on a near-daily basis as closely as that of any pitcher in recent memory.

So, after four starts, 13⅔ innings pitched and 64 batters faced, what have we learned? This sample is hardly large enough to make any drastic declarations about his career long-term, let alone the remainder of this season. But it’s enough to get an early gauge on Sasaki’s tendencies, what has worked well for him and what he’ll need to improve upon as his rookie season progresses.

Let’s dive in.

The stuff

Across his four seasons in Japan, Sasaki relied almost exclusively on three pitches: a high-90s four-seam fastball, a mid-80s slider and a spectacular splitter in the 88-89 mph range that was widely regarded as one of the most devastating off-speed pitches on the planet.

Via DeltaGraphs, here’s a look at how Sasaki’s arsenal evolved during his time in NPB:

• 2021

  • Fastball: 60% usage, 95 mph average

  • Splitter: 21%, 88 mph

  • Slider: 18%, 86 mph

• 2022

  • Fastball: 56%, 98 mph

  • Splitter: 34%, 89 mph

  • Slider: 5%, 88 mph

  • Curveball: 5%, 80 mph

• 2023

  • Fastball: 51%, 99 mph

  • Splitter: 35%, 89 mph

  • Slider: 14%, 88 mph

• 2024

  • Fastball: 46%, 97 mph

  • Splitter: 28%, 88 mph

  • Slider: 26%, 84 mph

The splitter has always been Sasaki’s preferred secondary offering, and he leaned on his fastball less in his final season in Japan. Perhaps that was a response to his slight dip in velocity in 2024, a trend Sasaki named during his free agency as something he was focused on fixing with his new team.

With his prior pitch mix in mind, what has Sasaki’s repertoire looked like as a major leaguer?

• Fastball: 57%, 97 mph

• Splitter: 29%, 85 mph

• Slider: 14%, 83 mph

The usage of Sasaki’s four-seamer has been restored closer to where it was earlier in his career, while his slider usage has sunk back to a distant third. The velocity, while still ranking in the 90th percentile among MLB arms, has yet to tick back up to the heights exhibited in 2023. Perhaps more notably, the average velocity for Sasaki’s splitter and slider are both a few notches below where they were in Japan. It’s likely too early to put too much stock into the radar gun readings as Sasaki continues to build up his workload, but these early marks will be worth revisiting later this summer.

Velocity aside, the arrival of Sasaki's standout splitter and its heavy dose of deployment is a compelling data point in a league-wide trend: Splitter usage has spiked significantly across baseball in recent years. From 2015 to 2022, splitters never accounted for more than 1.9% of the total pitches thrown in MLB during the regular season. But so far this year, 3.8% of pitches thrown have been splitters — a jump Sasaki has contributed to.

Even with the increased usage of splitters league-wide, Sasaki’s distribution of pitches makes his arsenal relatively unique, especially for a starting pitcher. He’s one of just a handful of starters who rely on a splitter as their go-to secondary pitch, along with fellow Japanese aces Yoshinobu Yamamoto and Shota Imanaga. But there’s really only one starting pitcher whose repertoire closely mirrors Sasaki’s specific balance of offerings, and that’s Blue Jays right-hander Kevin Gausman:

• Fastball: 56%, 94 mph

• Splitter: 32%, 86 mph

• Slider: 12%, 84 mph

It’s a strikingly similar pitch mix, though there are differences in the two pitchers’ release points and movement profiles. Sasaki throws much harder and from a higher arm angle, while Gausman’s pitches have markedly more spin across the board. Still, Gausman’s splitter-forward attack could serve as a rough template for the genre of pitcher Sasaki could grow into.

There are also a few crucial pieces of context to keep in mind when evaluating Sasaki’s stuff moving forward. For one, the evolution of his pitch mix is an ongoing process, one that is sure to be influenced by his new environment. MLB uses a different ball than NPB, one that is slightly larger and less tacky. Sasaki is still in the early stages of figuring out how his pitches move when thrown with the MLB ball, and he’s in the early stages of understanding how his repertoire plays against the best hitters on the planet, who are far more used to high-end velocity than Sasaki’s foes in NPB. He’ll also surely continue to alter his attack plan depending on his opponent; we’ve seen him face only three teams so far, including the Cubs twice.

Gina Ferazzi via Getty Images

The results

A generous interpretation of Sasaki’s performance thus far is that he has been effectively wild. His 3.29 ERA suggests that he has managed to keep opponents relatively in check despite his severe strike-throwing shortcomings, as evidenced by an MLB-high 20.3% walk rate and a 50% first-pitch strike rate that also ranks among the worst in baseball. A more pessimistic evaluation of the young righty would insist that this degree of wildness is wholly unsustainable if he is to remain a viable candidate to start for the Dodgers on a regular basis, not to mention down the stretch as the stakes continue to climb.

The truth is likely somewhere in between these initial assessments. No, Sasaki cannot continue to walk one-fifth of the batters he faces and expect to find success as a big-league starter. Sure, Luis Gil won AL Rookie of the Year with the highest walk rate in baseball (min. 100 IP) last season, but he was walking only 12% of opposing batters. Sasaki will need to rein in his control considerably, so it’s encouraging that his strike-throwing has improved with each start, enabling him to go deeper into games:

• March 19 vs. Cubs: 3 innings, 56 pitches, 25 strikes (45%)

• March 29 vs. Tigers: 1⅔ innings, 61 pitches, 32 strikes (52%)

• April 5 vs. Phillies: 4 innings, 68 pitches, 41 strikes (60%)

• April 12 vs. Cubs: 5 innings, 81 pitches, 50 strikes (62%)

At the same time, there's some solace to be found in the fact that most of Sasaki’s issues thus far have been self-inflicted. Yes, his proclivity to issue free passes has resulted in a stressful amount of traffic on the bases, but it’s not like opposing batters have been knocking him around the ballpark; Michael Busch’s home run on Saturday was the first extra-base hit Sasaki had surrendered in four starts.

Also, Sasaki’s much-hyped splitter has largely lived up to the hype, exhibiting unprecedented movement and registering a 46% whiff rate that already rates among the best of any individual offering in MLB. His heater, however, has not demonstrated nearly the same level of effectiveness: Among 63 pitchers who have thrown at least 100 four-seamers, Sasaki’s 11.8% whiff rate on his fastball ranks 58th. It’s worth noting that his teammate Yamamoto ranks 62nd on the same list, but Yamamoto’s far superior command and deeper arsenal have enabled notably more success so far this season. That’s a reminder that pitchers can succeed without getting swing-and-misses on their fastball, but they need to do a lot of other things well.

If Sasaki’s fastball continues to be more hittable in MLB than it was in NPB, the development of his slider will become paramount as an alternate means to coax whiffs, alongside his splitter. More broadly (and importantly), if Sasaki and the Dodgers can continue to refine his command, that should elevate the effectiveness of all three pitches as opposing batters are forced to respect his ability to locate them in the strike zone.

What’s next?

If we assume that Sasaki will remain on his start-every-Saturday schedule, his next outing will come this weekend against the Rangers at Globe Life Field, followed by a home start on April 26 against the lowly Pirates. Texas is a fascinating foe for Sasaki, as the Rangers’ offense currently ranks 30th in MLB in walk rate and has underperformed severely relative to the talented personnel in place. How Sasaki’s control issues manifest against a lineup that has thus far been relatively unwilling to take free passes will be interesting, and we’ll see if his pitch count continues to increase.

For Sasaki, every start represents another chance to improve as he gradually learns what it takes to succeed at the highest level. He’s clearly still figuring out what works and what doesn’t against the best hitters on the planet, and his arsenal and command of it are sure to continue evolving in the months and years to come. That said, with the Dodgers already in the thick of a heated NL West race, Sasaki’s development into a reliable rotation option, rather than a work-in-progress rookie, might prove to be more important to the team’s collective success than previously anticipated — and that makes each and every one of his starts all the more intriguing as the season unfolds.