Yomiuri Giants right-hander Iori Yamasaki didn’t come into the 2025 season as one of Nippon Professional Baseball’s elite starters, but after a month of play, he’s pitching like it.
On Wednesday, the 26-year-old Kobe native delivered seven shutout innings against the Hiroshima Carp, extending his scoreless streak to 35, a new Central League record to open a season. The Giants are now 5-0 in his starts. The previous record of 31 scoreless innings was set by Etsuo Nakai of the Hanshin Tigers in 1963 and matched by Shoki Murakami in 2023. (Side note: Murakami finished the season with a 1.75 ERA and won Central League MVP).
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Few would have predicted Yamasaki would be the one to achieve such a feat. Last season, the pennant-winning Giants were led by a star-studded rotation in Tomoyuki Sugano, Shosei Togo, and Foster Griffin. Yamasaki, who debuted in 2022 after being drafted out of Tokai University in 2020, has been a steady presence in Yomiuri’s staff for three seasons, but his mediocre underlying numbers didn’t demand much notice. In fact, he posted a below-average Fielding Independent Pitching (FIP) and Expected Fielding Independent Pitching (xFIP) in two of the three years, relying more on mixing speeds and inducing soft contact for fairly consistent results.
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The key to Yamasaki’s newfound success has been his splitter. The usage rate of the pitch has nearly doubled from 16.3% in 2024 to 31.4% in 2025. The pitch has been revamped to have more of a “splinker” shape, allowing it to be paired better with his cutter and sinker, and he’s added a tick on almost every pitch in his arsenal.
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He’s sitting 92.0 mph on his four-seamer. The Called Strike plus Whiff rate (CSW%) on his splitter has increased from just 24.9% to an excellent 33.3%, and he’s now utilizing it as his primary offering across various counts and situations. His splits against lefties have also improved drastically as the splitter has produced a gaudy 77.8% ground ball rate.
Overall, he’s posted a 24.6% strikeout rate, 3.1% walk rate, and 56.0% ground ball rate through five starts. He leads all qualified NPB pitchers in ERA (0.00), Win Probability Added (1.82), and Chase rate (43.5%). He ranks second in WHIP (0.74), FIP (1.63), and WAR (1.1). He also sits in the top 15 in key metrics like K-BB% and CSW%.
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With Sugano off to the Majors, Togo struggling and demoted to the farm, and Griffin yet to make a start, Yomiuri’s rotation has looked vulnerable so far in 2025. But Yamasaki, alongside fellow youngsters Haruto Inoue (2.12 ERA, 2.08 FIP) and Yuji Akahoshi (2.77 ERA, 2.91 FIP), have stepped up in big ways, helping the Giants to the best record in the CL entering May. If Togo and Griffin return to form, Yomiuri could be looking at a potential super-rotation.
