BFA News

April 4, 2021

Researchers in Japan use supercomputer to analyze why forkballs drop

April 4, 2021 (Mainichi Japan)


TOKYO -- Why does the forkball drop? A team of researchers in Japan, including those at Tokyo Institute of Technology, announced that they have revealed through supercomputer simulations that the "negative Magnus effect" exerts a downward force on the ball. They explained that the forkball is thrown with a two-seam grip, and the seams on the ball create special airflows, causing the effect.

From a batter's perspective, with every rotation of the ball as it is thrown, four seams come into view across the face of the ball in the four-seam pitch, while two seams come into view during one rotation in the two-seam pitch, depending on how the pitcher grips the ball when throwing it. The reason the forkball -- a type of two-seam pitch -- drops was believed to be due to the ball rotating fewer times compared to a straight ball.

The pitcher usually grips the ball with fingers set on or across the seam and throws it with a backspin. Common straight balls by professional baseball players are thrown with the four-seam grip, and the ball seems to float upward. That is because of the Magnus effect, which exerts an upward force on an object proceeding with backspin rotation.

However, when the research team simulated airflows associated with forkballs on a supercomputer, they found the air flew in the direction that exerts a downward force for about a third of the rotating period -- in other words, they observed a "negative Magnus effect." Comparison between the four-seam pitch and the forkball, both delivered at a speed of 150 kilometers per hour with the same number of rotations, revealed that the two-seam forkball reaches a catcher as much as 19 centimeters lower than the four-seam ball.

Besides forkballs, in pitches like knuckleballs in which the ball drops, fewer rotations were the cause of the drop.

In professional baseball in Japan, Fukuoka SoftBank Hawks pitcher Kodai Senga is well known for his "ghost forkball," in which the ball drops suddenly, practically disappearing from the batter's view. Senga has revealed that he applies a bulletlike special "gyro rotation" to the ball. The research team also simulated Senga's ball rotation and demonstrated that his pitches drop more than common forkballs.

Takayuki Aoki, a research team member and a professor at Tokyo Institute of Technology, said, "Professional baseball players in Japan rely less on data compared to Major League Baseball players, but if they throw the ball while consciously calculating the rotation of the seams, their pitches may change."