Strengths and Weaknesses of Rintaro Sasaki’s Harakiri Swing at Stanford

Strengths and Weaknesses of a Cannon Aiming for the Majors

“When I look back at the results, I can’t say I’m satisfied at all, but I think it was good that I was able to fight through all 52 games.”

Rintaro Sasaki (20) of the prestigious Stanford University in the United States, who completed his first season on May 21 Japan time, reflected this way during the post-game interview.

Sasaki hit a record 140 home runs during his high school career at Hanamaki Higashi High School (Iwate Prefecture) and moved to the U.S. without going through the NPB draft. In his first year, he posted a batting average of .269 with 7 home runs and 41 RBIs. While the results are respectable, given his high school achievements, he likely isn’t satisfied. Takashi Kawamura, a specialist in sports motion analysis and a professor at the School of Health and Physical Education at the University of Tsukuba, discusses the strengths and weaknesses of the slugger aiming for the majors.

“He’s a hitter with a body type that has flexibility. He’s a left-handed power hitter similar to Munetaka Murakami of the Yakult Swallows. However, there are aspects of how he uses his body that need to be corrected.”

If only he can overcome his problems, he has enough potential

ChatGPT said:

Let’s follow Professor Kawamura’s analysis while looking at the sequential photos of Sasaki’s form.

“In the transition from ① to ②, he shifts his weight solidly onto his left foot, which gives him stability. Since his head position remains steady, it’s hard to throw off his balance. In ②, he lifts the bat from a horizontal position and swings it downward. This allows him to scoop up the ball and add loft, enabling him to hit it far.”

In ③, a key issue becomes apparent.

“His hips and shoulders are rotating at the same time. This prevents the energy from the lower body from being transferred properly to the upper body. Ideally, the hips should lead, creating a twist in the upper body. This smooth transfer of energy from the ground up is crucial. But in his case, the shoulders rotate too early, causing the grip to move forward prematurely.”

This premature grip movement creates inefficiencies in his motion between ④ and ⑤.

“The bat takes a longer path. Ideally, the bat head should come out as late as possible by building torque in the body. But in Sasaki’s form, the bat comes out too early, and he can’t wait on the ball. The grip moves in front of his stomach, resulting in a cramped ‘Harakiri Swing.’ The bat doesn’t accelerate properly, and the power isn’t effectively transferred to the ball.”

In ⑥, despite his advantageous physique—184 cm tall and weighing 114 kg—he isn’t fully utilizing it.

“Because of the early rotation, the bat ends up pointing toward first base before the finish. Even when he makes solid contact, the ball doesn’t fly straight and ends up slicing into foul territory. His inefficient movement is preventing him from maximizing his power.”

So, can Sasaki thrive in the majors?

“Most power hitters in the majors begin to make an impact around age 25. Until then, many spend years in the minors refining their skills. Sasaki should be viewed with a long-term perspective. If he can overcome the issue of his shoulders and hips rotating together, he definitely has the potential. I believe he could hit 20 home runs a year in the majors.”

Sasaki is still only a college freshman. He has plenty of time to grow into one of the premier sluggers in the majors.

From the June 27/July 4, 2025 issue of “FRIDAY”