Pitchers Shortening Their Arm Action and the Effects on Pitch Flight Data

The professional baseball landscape is ever-changing, and over the past few years it has emphasized the importance of player development. This has been well documented in books like The MVP Machine. As a result, teams are looking for different ways to create competitive advantages in this department to maximize player performance. One such area where players and staff are looking for improved performance are mechanical changes in a pitcher’s arm action, to a shorter, more efficient motion. Lucas Giolito is the poster boy for this recent trend. After struggling mightily in 2018, Giolito changed his arm action and turned in an All-Star season in 2019, good enough to finish 6^th in the AL Cy Young voting that year. However, after researching Giolito’s transformation, I discovered that this is not necessarily a new trend. Joe Kelly shortened his arm path during the 2016 season after being demoted to Triple-A by the Red Sox. In an article written by Lantz Wheeler discussing Giolito’s mechanical overhaul, he mentions how, then Cubs’ reliever, Neil Ramirez made the same change during the middle of the 2014 season, seemingly between outings.

For decades, cookie-cutter type approaches have been given to every pitcher or hitter with the expectation that since it worked for one athlete, it should work for all others. However, in my past experiences working with motion capture and biomechanical data, I have learned that this is not the way to yield the best results. No two athletes move the same. Chris Sale moves entirely differently than Marcus Stroman, and while this is an obvious distinction you get the point that is being made. Baseball as an industry has been understanding the importance of individualization in player development and utilizing motion capture and biomechanical data to learn more about how each athlete moves during their throwing motion. Therefore, when a pitcher changes their arm action, they are fundamentally changing how their body moves down the mound; a movement they have repeated thousands of times during their baseball life. This is highlighted by The Athletic in a piece by Nick Groke on Rockies’ Jeff Hoffman and his mechanical change at Driveline this past off-season, “Every small action led to others. His shortened arm movement needed a corresponding change to his legs. Timing was key and difficult.”

Knowing movement changes in the body occur when reconstructing an arm action, and using the ascension of Lucas Giolito as a marker, I decided to research if changing a pitcher’s arm action affects their pitch flight metrics. What I found was a resounding yes. Below is a list of the pitchers I found who substantially changed their arm action and the percent difference from their metrics before and after their mechanical transformation. For the purposes of this article, I omitted Robbie Ray, while he is another great example of this trend, over the course of the 2020 season he began gradually returning to his original arm action before completely going back to it altogether, which made it difficult to determine a cutoff point.

To repeat, the numbers in this table are representative of the percent change in values from before the arm action transformation to afterwards. For example, Jeff Hoffman’s curveball had a 25% reduction in horizontal movement, whereas Hoffman’s changeup had over a 13% increase in horizontal movement from changing his arm motion. In each column, the highlighted values represent the maximum increase and maximum decrease that resulted from the change being made. To expand, Joe Musgrove’s changeup had the largest increase in horizontal movement at over 66%. (One thing to note is the blank values in spin for Neil Ramirez, spin rates began being captured publicly in 2015). As you can see though, a pitcher changing their arm action has an effect on how their pitches move afterwards, and sometimes the difference is quite profound.

The biggest takeaway from my research is why the players made these changes compared to what the changes actually did. Giolito was once a top prospect in the game. One who the Nationals seemingly gave up on and was looking like a bust after coming off a 2018 season that was historically bad. He often struggled with his control, walking nearly 11% of batters in his career through the end of 2018. During the off-season after the 2018 season, Giolito overhauled his arm action, and it produced better results. His walk rate is now down 2% in the past two seasons from his pre-transformation rate, and the pitch chart below shows his pitches have been more centralized.

Lucas Giolito 2018 Pitch Chart

Lucas Giolito 2019 Pitch Chart

Giolito’s command improved, but his pitches began behaving differently, which was not his original goal at the beginning of his mechanical overhaul. The table below shows all four of Giolito’s pitches from 2019 and their percent change from 2018. Every single pitch’s characteristics changed. In the same Lantz Wheeler article mentioned earlier, Giolito talks about the changes to his arm action and how he feels about it, “It’s a cleaner action. I feel like I’m much more consistent getting on top of the ball, especially my fastball. I notice my fastball spinning better, more efficiently, the data backs that up…It just feels better.” The data most certainly backs that up, by getting more on top of his fastball he had an 11% increase in spin rate, a 16% increase in vertical movement, and lowered his horizontal movement by 2.5%. However, his fastball was not the only pitch effected. His slider and curveball lost horizontal movement and added depth, and in the case of his slider, a lot of it. He was also able to kill spin on his bread and butter pitch, his changeup, by over 5%. But perhaps one of the biggest changes was the uptick in velocity on his fastball, as a result of his more efficient arm path. His average velocity was up 1.8%, or 1.7 MPH, from 2018-2019. Giolito throws his changeup as more of a speed differential pitch and the added velocity on his fastball, combined with a slight decrease in velocity on his changeup, increased the average differentiation between the two pitches from 10 MPH to 12MPH. His change in his body movement down the mound directly affected how his pitches acted. Essentially, he was a completely different pitcher than the one he had been his whole life.

After Giolito’s success, other pitchers began to mimic his transformation. Jeff Hoffman, Joe Musgrove, and Joe Ross all watched closely and tinkered with their own arm actions to find the consistency that Giolito was searching for months earlier. In a piece by Jason Mackey for the Pittsburgh Post-Gazette, Musgrove talks about the change he felt from a shorter arm action, “It cleaned up the arm path. It made my breaking ball better. The spin on my fastball got better.” Again, the data backs this up, Musgrove increased the vertical movement on his slider by over 350% and his fastball spin rate increased by 1.2%. Hoffman and Ross also experienced noticeable changes. Hoffman had the largest decrease in vertical movement on any pitch in my research at a 27% drop on his changeup, and Joe Ross’s vertical release point increased by 1.2% or more for every pitch type.

While the quantifiable changes to both control and pitch movement are positives for most pitchers, there were unintended benefits that came from the mechanical transformations as well. Many of the pitchers commented on how much healthier they felt, Giolito said, “It feels better, I feel healthier” and Musgrove said, “The arm recovery got better”. More biomechanical data and research is needed, and it’s coming as more teams and facilities implement motion capture systems, but perhaps a shorter arm action tends to lead to more efficient body movement, causing pitchers to feel better and, most importantly, have an improved chance at staying healthy.

While my research was designed around the instances where this mechanical change helped, there are certainly cases, and will be more in the future, where this transformation has adverse effects on pitchers. Robbie Ray attempted the same mechanical overhaul heading into the restart of the 2020 season. He ended up with the highest walk rate, Barrel%, and exit velocity of his career, and switched back to his previous arm path before the season ended. Changing one’s arm action is not a one-stop-shop to finding the consistency a pitcher is looking for. It can work, and I exemplified how so above, but as seen in the case of Jeff Hoffman, there are additional changes that need to be made to the body that result from shortening the arm path.

In the end, my research found exactly what I thought it might, that changing the arm action of a pitcher does in fact change how their body moves down the mound, and, as a result, changes how the ball moves. As player development, and the inclusion of motion capture, has progressed, individualization is paramount for a player’s success. No two athletes move the same, so a cookie-cutter type approach does not work. While this mechanical change is not an answer for everyone, it has shown it can produce positive results and does change the pitcher’s ball flight data. Like everything, this is just another tool in the toolbox for developing players and maximizing their potential.