San Francisco Giants first baseman Rafael Devers has been struggling against the four-seam fastball. He is 6 for 37 against the pitch, resulting in a batting average of .162.

This is not the first season Devers has underperformed with this pitch. He has hit .258 with 69 home runs off four-seam fastballs since 2021. His outcomes correlate with the amount of pitch movement before reaching the catcher.

He struggles the most with four-seam fastballs exhibiting minimal horizontal movement. This pattern likely relates to his swing mechanics. Devers’ timing at the plate depends on a one- or two-second leg kick. 

He begins his leg kick when the opposing pitcher separates the baseball from his glove. Devers then holds his leg in the air for one to two seconds before planting his foot. Once his foot is down, he brings the bat through the strike zone to attempt a hit.

Four-seam fastballs with limited horizontal movement disrupt the timing of Devers’ leg kick. On April 19, 2026, facing Miles Mikolas of the Washington Nationals in the top of the third inning, Miles threw a 93 mph fastball with 6.4 inches of glove side movement. Devers finished his leg kick when the ball was only two feet from the catcher, making it difficult to bring his bat through the zone in time.

Four-seam fastballs with greater horizontal movement allow Devers more time to finish his leg kick and get his bat into the strike zone. On April 22, 2026, he faced the Los Angeles Dodgers.

Shohei Ohtani delivered a 99 mph fastball with 9 inches of arm-side run. The additional movement allowed Devers to complete his leg kick when the pitch was about three or four feet from home plate, resulting in an opposite-field hit.

This challenge is not isolated; Devers has collected 263 hits off four-seam fastballs. These hits average 8.1 inches of glove-side movement and 3.5 arm-side movement. When making outs, the average glove-side and arm-side movement drops to 3.5 and 7.4 inches, respectively.

Given these patterns, Devers should focus on targeting other pitchers, as adjusting to these four-seam fastballs may be too challenging for him. For instance, Rafael Devers has hit 323 against the curveball since 2021. The pitch has 9 inches of glove side movement and 4 inches of arm side movement.