Earlier this season baseball writer Travis Sawchik posted a thread on Twitter about how the Yankees’ Jameson Taillon was one of several MLB pitchers who had shortened their “arm circle” to theoretically protect the arm and improve performance. Sawchik wrote:
“The shorter ‘arm circle’ or ‘elbow spiral’ is gaining popularity (Jameson Taillon and Aaron Civale are among the new adopters) and when you look at the success guys like [Lucas] Giolito, [Trevor] Bauer, [Shane] Bieber & [Zach] Plesac have had with a shorter arm action it makes a lot of sense.”
Without getting into a lengthy discussion on biomechanics, the short version is that keeping the hand and elbow closer to the body when throwing (more similar to a quarterback throwing a football) will both create more leverage from the torso, and put less stress on the arm.