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.
The pair started out struggling but have both recently improved.
After a down first month, both have shown a monthly improvement. I wanted to see if there was more to this improvement.
Note: After digging around, I nearly didn’t finish this article. There just wasn’t a solid conclusion but I figured others might want to know that result. So I’ll trudge forward with limited success.
I investigated the pair’s data (with StatCast) and many other TJS recipients (without StatCast). I found almost nothing. It is just a small data sample and the StatCast data is still useless with a sample size of two. There was one small glimmer of hope, the standard Hard Hit Rate. I noticed the rate normally climbed during their first season back to previous levels. For example, here are Seager’s and Ohtani’s improvements.
The monthly improvement follows the normal ramp-up narratives noted in spring training and after injuries for hitters. Some recent reading I’ve completed puts the improvement more on the mental side than physical.
Before I go any further, I must fully disclose I’ve got just one quote from one book on the subject. I’m trying to find out more on the subject to understand it better, but any available literature is deep. It’s about the brain and written by scientists. There are no Michael Lewises among these authors. The general idea is that it takes over a month for any person to relearn a skill with a fully healthy body.
The best/understandable “money” quote from The Performance Cortex by Zach Schonbrun states juggling but the chapter mentions any hand-eye activity including quite a bit on baseball:
But Wolpert would note that it takes a ton of effort – a month and a half of intense juggling training for some meager changes in the fine architecture of our white matter – just to find a way to reduce some aspect of noise.
The key is that the white matter (brain’s nerve cell structure) forms a network to perform a task and if anything changes (e.g. injury), the brain structure must change to learn this new skill. It would be the same change a batter would need to go through to learn a new stance or a new wind up for a pitcher.
These hitters have been spending months rebuilding up a new elbow and the brain changing along the way. Once they are 100% healthy, the brain is still catching up. The time is not 100% set at 1.5 months. It could be less or more. I’m trying to find more information on this topic but either way, don’t ever be surprised any player still struggles even though they feel 100% healthy.
Sorry the large side topic, so back to the original question. I just don’t know for sure when these hitters returning from TJS will be 100% but a couple of signs point to a month or two to get up to speed. This call could be proven wrong by season’s end.
Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won three FSWA Awards including on for his MASH series. In his first two seasons in Tout Wars, he's won the H2H league and mixed auction league. Follow him on Twitter @jeffwzimmerman.