iTranslated by AI
Yusei Kikuchi's 'Slider Revolution' (2019-2025) Seen Through Statcast Data
Introduction
Pitcher Yusei Kikuchi has played for four teams since moving to MLB in 2019: the Mariners, Blue Jays, Astros, and Angels. In his NPB days, his repertoire consisted mainly of four-seams and sliders. However, by 2025—his seventh year in MLB—his pitching style has shifted significantly, with the slider surpassing the four-seam as his most frequently thrown pitch.
In this article, we will track the evolution of Kikuchi's pitch mix over his seven-year career using pitch data from Statcast (MLB's high-precision tracking system). We will specifically focus on the "Slider Revolution" that occurred following his trade to the Astros in July 2024. Please note that this analysis highlights trends observable from the data and does not definitively state the pitcher's personal intentions or strategies.
Career Overview
| Period | Team | Games Started | Pitch Count | Avg Velocity (All Pitches) | Number of Pitch Types |
|---|---|---|---|---|---|
| 2019 | SEA | 32 | 2,721 | 87.3 mph | 5 |
| 2020 | SEA | 9 | 795 | 91.4 mph | 4 |
| 2021 | SEA | 29 | 2,562 | 90.5 mph | 5 |
| 2022 | TOR | 32 | 1,844 | 91.1 mph | 6 |
| 2023 | TOR | 32 | 2,818 | 90.5 mph | 7 |
| 2024 1st Half | TOR | 22 | 1,955 | 90.7 mph | 4 |
| 2024 2nd Half | HOU | 10 | 971 | 89.9 mph | 4 |
| 2025 | LAA | 33 | 3,109 | 88.5 mph | 6 |
In 2025, he recorded a career-high 33 starts and 3,109 pitches.
Pitch Mix Evolution: Three Phases
The evolution of Kikuchi's pitch repertoire over the past seven years can be broadly divided into three phases.
Phase 1: The Cutter Era (2019-2021, Mariners)
| Pitch Type | 2019 | 2020 | 2021 |
|---|---|---|---|
| FF (Four-seam) | 48.9% | 37.7% | 35.8% |
| FC (Cutter) | 0.0% | 40.0% | 32.9% |
| SL (Slider) | 28.0% | 16.0% | 20.2% |
| CU (Curveball) | 15.4% | 0.0% | 0.4% |
| CH (Changeup) | 7.6% | 6.3% | 10.7% |
In 2020, the cutter (FC) suddenly accounted for 40.0% of his pitches, and it remained a major pitch in 2021 at 32.9%. This period was characterized by the "two pillars" of his four-seam and cutter.
Phase 2: Four-seam Dominance (2022–2024 1st Half, Blue Jays)
| Pitch Type | 2022 | 2023 | 2024-TOR |
|---|---|---|---|
| FF | 50.5% | 45.2% | 49.6% |
| SL | 30.3% | 26.3% | 17.4% |
| CU | 0.3% | 18.9% | 22.1% |
| CH | 13.4% | 9.1% | 10.9% |
| FC | 5.4% | 0.0% | 0.0% |
With his move to the Blue Jays, the cutter was almost entirely phased out. Centered around a four-seam usage of approximately 50%, he transitioned to a balanced four-pitch mix as his curveball was reintroduced in 2023. In the first half of 2024, his slider usage dropped to 17.4%, leading to a higher dependency on the four-seam.
Phase 3: The Slider Revolution (2024 2nd Half–2025, Astros → Angels)
| Pitch Type | 2024-TOR | 2024-HOU | 2025 |
|---|---|---|---|
| FF | 49.6% | 41.8% | 34.9% |
| SL | 17.4% | 37.2% | 36.2% |
| CU | 22.1% | 9.4% | 15.4% |
| CH | 10.9% | 11.6% | 12.1% |
Following his trade to the Astros in July 2024, his slider usage doubled from 17.4% to 37.2% (+19.8 points). With the Angels in 2025, his slider (36.2%) surpassed his four-seam (34.9%), marking the first time in his career that the slider has become his most frequently thrown pitch.
Detailed Analysis of the Slider
Let's look at the changes in the quality of the slider, not just its usage rate.
| Period | Usage Rate | Average Velocity | Spin Rate | Whiff Rate | xBA Against |
|---|---|---|---|---|---|
| 2022 | 30.3% | 86.6 mph | 2,355 rpm | 31.0% | .366 |
| 2023 | 26.3% | 88.7 mph | 2,427 rpm | 28.0% | .361 |
| 2024-TOR | 17.4% | 89.0 mph | 2,412 rpm | 27.8% | .343 |
| 2024-HOU | 37.2% | 87.5 mph | 2,380 rpm | 28.1% | .346 |
| 2025 | 36.2% | 87.0 mph | 2,295 rpm | 23.1% | .344 |
While the whiff rate slightly decreased to 23.1% in 2025, the xBA against has remained stable between .343 and .346, suggesting that it is functioning as a pitch to induce contact for outs. It is noteworthy that the quality of contact has not deteriorated even as the usage rate doubled.
52% Sliders to Left-Handed Hitters
Because Kikuchi is a left-handed pitcher, the slider follows a trajectory that breaks away from left-handed hitters (LHH). While left-handed pitchers typically don't rely as heavily on the slider against LHH, his 2025 pitch distribution shows an interesting pattern.
2025 Pitch Mix Against LHH:
| Pitch Type | Usage Rate | Whiff Rate |
|---|---|---|
| SL | 52.4% | 23.6% |
| FF | 32.7% | 19.8% |
| CU | 10.5% | 34.3% |
| SI | 4.4% | 20.0% |
More than half of his pitches to left-handed hitters are sliders. He does not use a changeup, sticking to a simple three-pitch repertoire of slider, four-seam, and curveball.
On the other hand, against right-handed hitters, he uses a balanced four-pitch mix: FF 35.7%, SL 32.6%, CU 16.6%, and CH 14.7%.
Trends in Four-Seam Velocity
Next, we examine the velocity trends of his four-seam (FF).
| Period | Average Velocity | Spin Rate |
|---|---|---|
| 2019 | 92.5 mph | 2,096 rpm |
| 2020 | 95.0 mph | 2,172 rpm |
| 2021 | 95.1 mph | 2,214 rpm |
| 2022 | 94.9 mph | 2,271 rpm |
| 2023 | 95.1 mph | 2,339 rpm |
| 2024-TOR | 95.6 mph | 2,276 rpm |
| 2024-HOU | 95.2 mph | 2,322 rpm |
| 2025 | 94.8 mph | 2,185 rpm |
His average velocity rose significantly from 92.5 mph in 2019 to 95.0 mph in 2020 and has remained stable within the 94.8–95.6 mph range since then. The 94.8 mph recorded in 2025 is well within his career average range.
Velocity Changes by Inning
While Kikuchi achieved a career-high 33 starts in 2025, how much did his velocity drop as the game progressed?
| Inning | 2023 | 2024-TOR | 2024-HOU | 2025 |
|---|---|---|---|---|
| 1st | 95.0 | 95.9 | 95.3 | 95.2 |
| 3rd | 95.2 | 95.9 | 95.2 | 95.1 |
| 5th | 95.0 | 95.3 | 95.2 | 94.5 |
| 7th | 95.1 | 95.1 | 94.5 | 94.3 |
In 2025, there was a decrease of -0.9 mph from the 1st inning (95.2) to the 7th (94.3). This is not a drastic drop, demonstrating the stamina required to continue pitching effectively through seven innings.
Improvement in Batted Ball Quality
Let's look at the quality of contact allowed by period.
| Period | xwOBA | Hard Hit% | Avg Exit Velo |
|---|---|---|---|
| 2019 | .384 | 28.7% | 84.5 mph |
| 2021 | .419 | 28.4% | 84.3 mph |
| 2022 | .456 | 26.9% | 83.6 mph |
| 2023 | .400 | 25.9% | 83.5 mph |
| 2024-HOU | .382 | 25.3% | 82.1 mph |
| 2025 | .385 | 25.1% | 83.5 mph |
His xwOBA has steadily improved from .456 in 2022 to .385 in 2025. His Hard Hit% also shows a downward trend, from 28.7% (2019) to 25.1% (2025), suggesting that he is becoming increasingly capable of preventing hard contact year by year.
In particular, his xwOBA of .382 and Hard Hit% of 25.3% during his tenure with the Astros (2024-HOU) are strong marks, and the data suggests that the trade may have been the catalyst for his improved performance.
Whiff Rates Showing a Downward Trend
On the other hand, there are visible challenges regarding the whiff rates for all pitch types.
| Pitch Type | 2023 | 2024-TOR | 2024-HOU | 2025 |
|---|---|---|---|---|
| FF | 23.1% | 24.0% | 26.5% | 18.0% |
| SL | 28.0% | 27.8% | 28.1% | 23.1% |
| CH | 18.1% | 29.7% | 41.9% | 24.6% |
| CU | 28.0% | 26.3% | 25.0% | 23.8% |
In 2025, whiff rates for both the FF (18.0%) and SL (23.1%) have decreased. Meanwhile, during his time with the Astros, his changeup recorded a phenomenal whiff rate of 41.9%, which has settled back to 24.6% in 2025.
Overall, there is a visible trend towards a "pitch-to-contact" style—inducing ground balls and weak contact rather than strictly seeking strikeouts. Considering the improvement in batted ball quality, this may be an intentional shift.
Put-Away Pitches with Two Strikes
Changes are also evident in his pitch selection after getting ahead in the count.
| Period | FF | SL | CU | CH | Pitch with Highest Whiff Rate |
|---|---|---|---|---|---|
| 2023 | 39.6% | 36.8% | 15.3% | 7.5% | CU 31.0% |
| 2024-TOR | 39.7% | 25.6% | 19.1% | 15.7% | CH 39.5% |
| 2024-HOU | 42.9% | 36.6% | 9.5% | 11.0% | CH 44.4% |
| 2025 | 36.7% | 30.8% | 14.7% | 16.7% | SL 27.2% |
The 44.4% whiff rate on his changeup with two strikes during his time with the Astros is remarkable. In 2025, his four-seam percentage has dropped, shifting toward a more even usage of all four pitches.
Performance by Times Through the Order
| Times Through Order | 2023 | 2024-HOU | 2025 |
|---|---|---|---|
| 1st TTO Whiff Rate | 26.0% | 25.8% | 20.9% |
| 2nd TTO Whiff Rate | 26.0% | 31.9% | 23.0% |
| 3rd TTO+ Whiff Rate | 22.0% | 26.8% | 20.5% |
| Times Through Order | 2023 xwOBA | 2024-HOU xwOBA | 2025 xwOBA |
|---|---|---|---|
| 1st TTO | .416 | .393 | .405 |
| 2nd TTO | .385 | .367 | .363 |
| 3rd TTO+ | .399 | .386 | .386 |
In 2025, the 3rd TTO xwOBA of .386 is worse than the 2nd TTO (.363), but it shows improvement compared to 2023 (.399). The "Slider Revolution" following his move to the Astros may be contributing to his improved resilience during the third time through the lineup. By diversifying his pitch usage, he likely makes it more difficult for hitters to adjust in their second and third plate appearances.
Summary
The Statcast data for Kikuchi from 2019–2025 revealed the following trends:
- Three Phases: The Cutter Era (2019–21) → Four-seam Dominance (2022–24 1st Half) → Slider-centric (2024 2nd Half–25)
- The Slider Revolution: Slider usage doubled from 17.4% to 37.2% after his move to the Astros. In 2025, it became his most frequent pitch, surpassing the four-seam (36.2% > 34.9%).
- Improved Batted Ball Quality: xwOBA .456 (2022) → .385 (2025), Hard Hit% 28.7% (2019) → 25.1% (2025).
- Declining Whiff Rates: FF 23.1% → 18.0%, SL 28.0% → 23.1% (2025). This suggests a shift toward a style that induces weak contact rather than strictly seeking strikeouts.
- 52% Sliders to LHH: A bold pitch distribution pattern for a left-handed pitcher.
- Durability with 33 Starts: Stable performance with a velocity drop of only -0.9 mph through the 7th inning.
Kikuchi's career appears to be an intriguing example showing how a pitcher can alter their performance by changing their pitch composition. The data reflects how he has continued to evolve while being influenced by pitching coaches and analytics departments across four different teams.
Reproduce the Analysis in Google Colab
The analysis in this article can be reproduced using the following notebook. By changing the PITCHER_ID, it can also be applied to other pitchers.
Discussion