Expectation for Hitters Returning from Tommy John
Last season at BaseballHQ ($$), I found the expected results for hitters returning from Tommy John surgery (TJS). The research was completed with traditional stats and no StatCast information was utilized. The reason was that only one regular, Christian Vazquez, had Tommy John surgery since there was publicly available StatCast data. That changed when five hitters had the surgery last year. With the return of Didi Gregorius, all have made it to the majors. Sadly the early returns are unspectacular with Corey Seager and Shohei Ohtani struggling.
In his first three seasons, Seager posted a .876 OPS but past two seasons it has only been a .793 OPS. I included last season because he struggled while trying to play through the injury. For Ohtani, he posted a .925 OPS last year and just a .742 OPS this season. These values line up with the original TJS article.