TEMPE, Ariz. — In the fall of 2013, Andrew Heaney began to pitch from the first-base (or arm) side of the rubber. For the then-22-year-old left-hander, it was a small change, not 24 inches from his old manner. But it produced a significant, positive result: He dominated the Arizona Fall League and made his big-league debut before the subsequent summer.



His career trending upward, he opened 2016 as the Angels’ No. 2 starter, matching up with Jon Lester in the season’s second game. Three innings in, Heaney tore the ulnar collateral ligament in his left elbow. He tried, unsuccessfully, to avoid Tommy John surgery, succumbing that July. As he readied to mount his comeback, the Angels presented him a suggestion to switch back.



“Statistically, if you’re on the glove side of the rubber, you’re not cross-firing as much,” Heaney recalled club officials relaying. “A lot less torque and leverage on your arm. It’s...