Does Aroldis Chapman’s posture affect his command on the mound?

After the Yankees’ won their series opener against the A’s on Thursday night, Aaron Boone told reporters that Aroldis Chapman made a change to his posture on the mound after discussing his mechanics and going over film before the game with pitching coaches Matt Blake and Mike Harkey. Chapman had struggled with command during the Yankees’ previous series against the Braves, and before Chapman secured the last out of Thursday night’s game I’m sure there were plenty of fans who feared he would implode on the mound again.

Boone’s remark about Chapman’s meeting with Blake and Harkey reminded me that Twitter user @HoodieGleyber had observed a change in Chapman’s posture, noting that he looked more upright before beginning his windup than he did in his most recent outings in Atlanta.

Sports Illustrated’s Max Goodman also noted Boone’s comment about Chapman’s posture and posted photos demonstrating the contrast in his stance on the mound on Thursday, versus how he stood before his final pitch in Atlanta.

Pitchers make small adjustments all the time, but the simplicity of Chapman’s tweak made me curious about the relationship between Chapman’s posture and his control issues. Does he always curl up and lean too much when he doesn’t have his stuff? Is his leaning posture just a bad habit? I decided to watch footage — both recent clips and in older video — of Chapman’s pitching in order to observe his posture and pre-windup mechanics.

It quickly became obvious, upon watching video of Chapman’s pitching — both successful outings and blown saves — that Chapman works at a slower pace when he is having difficulty locating his pitches. During outings when he doesn’t trust his four-seamer, in particular, he takes more time between pitches. He also bends more at the waist. The top photo in the image below is from Chapman’s most recent outing on Thursday night. His torso is closer to being perpendicular with the mound. In the bottom photo, captured during his blown save against the Angels on June 30th, his torso leans forward at a sharper angle and he appears more crouched.

Let’s see what Chapman looked like on the mound in another one of his blown saves from this year. The image on top is from June 23th, when Chapman blew the save against the Royals. The bottom image is from his appearance against the Red Sox on August 17th, 2020.

When a pitcher starts to go into his windup, maintaining an upright spine angle makes it easier to establish a consistent release point. Leaning or bending the torso out of alignment creates a barrier to pitch repetition and inhibits a pitcher’s ability to commit movements to muscle memory. The lack of consistency that occurs as a result of poor posture can then have a negative impact on a player’s pitch command. Simply put, poor posture makes it pretty difficult to replicate a release point. Bending forward causes a pitcher’s shoulders to rotate horizontally, which also puts unnecessary stress on the throwing shoulder and elbow.

The contrast in the positioning of his torso is especially noticeable in these images from Chapman’s outings on April 21st, 2019, and May 1st of this season, respectively.

In all likelihood, Chapman’s bent posture is one among several factors contributing to his inconsistency on the mound. Even so, after conducting a thorough, albeit unscientific, analysis of about 20 of Chapman’s outings, it appears as if there is some kind of correlation between his leaning too far forward and his struggles with command.