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Secrets of Shohei Ohtani's Best 'Sweeper' Analyzed by Supercomputer Fugaku

Some of Shohei Ohtani's pitches are famously difficult to hit, but his sweeper is truly unique. Researchers used the Fugaku supercomputer to learn how it works.



Shohei Ohtani
Los Angeles Angels right-hander Shohei Ohtani fires a pitch to an Oakland Athletics batter on Opening Day on March 30 at Oakland Coliseum. (©KYODO)

Shohei Ohtani's remarkable breaking ball, known as the "sweeper," exhibits a pronounced lateral curve while maintaining minimal vertical drop. This unique characteristic is attributed to the direction of the ball's rotational axis aligning with its trajectory. 

Research teams used the Fugaku supercomputer to analyze it. Then on May 29, the Tokyo Institute of Technology revealed the secret hidden mechanism of this remarkable pitch. Their analysis showed the tilted axis of rotation also created an upward force on the ball, leading to its unique movement.

This diagram shows the trajectory of Major League Baseball player Shohei Otani's "Sweeper." His pitch is reproduced here by supercomputer "Fugaku." From the front (gray dots) to the direction of the batter (white dot), the analysis shows the ball curving to the left without falling. (Provided by Professor Takayuki Aoki of Tokyo Institute of Technology).

What is a Sweeper?

The sweeper gained recognition when Shohei Ohtani showcased it during the Japan national team's victory in the World Baseball Classic in March. And while a sweeper is a type of slider, a conventional slider curves with a gradual drop. 

Analysis of Ohtani's pitching data also shows his sweeper is unique. It is a variety of slider that bends sideways but with a minimal downward trend. Why this phenomenon occurs remains a mystery. 

Shohei Ohtani struck out 156 batters in 130 1/3 innings in 2021. (Gary A. Vasquez/USA TODAY SPORTS)

Fugaku Analyzes Ohtani's Pitches

The research team utilized the Fugaku supercomputer to try to unravel the secrets. First, they calculated the surrounding airflow and trajectory of the ball by altering the rotation speed and angle of the axis of rotation. 

Eventually, they tilted the rotation axis by 50 to 60 degrees in the batter's direction. As a result, this tilted axis generated an airflow that pushed the ball diagonally upward from behind. In this way, they were able to replicate Shohei Ohtani's pitches. 

MLB.com has documented the use of the sweeper since the start of the 2022 season. According to the website, 99 MLB pitchers had thrown the pitch as of April 19, 2023.


(Read the report in Japanese.)

Author: The Sankei Shimbun

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