Lingering Effects of Elbow & Shoulder for Pitchers

I don’t know for sure where I read or heard it, but an analyst mentioned they would never go near Luis Severino this season in drafts because of last season’s major shoulder injury. This claim is something I can investigate on the surface to see if anything sticks. Besides the numbers for shoulder injuries, I included the pitchers with elbow injuries.

For the analysis, I took the players who were on the IL for a shoulder or elbow injury in year one and then compared their next season projection and results. I had matching data going back to 2010 but didn’t use 2018 IL data because for some reason I didn’t clean up the last year’s data.

Then, I  took the average, median, and weighted average of each pitcher and grouped them by the days they were on the IL the previous season. These of these composite values each provide a unique insight. The average values can be quite a bit worse because one rogue 27.00 ERA can throw everything off. The median value is the one I prefer because it’s the 50 percentile results and it is how the random pitcher will perform. Finally, I included the weighted averages based on the innings pitched that season. The value is full of survivor bias since the pitchers who are getting good results will be allowed to keep throwing. Those that suck are in AAA.

I started cutting and dicing the groups to see if any interval stood out. I found a couple that work.

Starting with the shoulder injuries, I found the line at 100 days missed and here are the results.

While the WHIP didn’t move much, a 0.39 jump in ERA is nuts. Even the weighted value had a decent jump.

These values didn’t surprise Dr. Jesse Morse, “Shoulders are a complicated pain in the ass. Shoulders if you’re lucky, calm down with just a steroid injection and rehab, if that’s not enough then it’s not pretty.” Any long IL stay for a shoulder injury is not ideal.

And for reference, here are the pitchers who spent over 100 days on the IL for shoulder injuries last season.

When I moved over to the elbow injuries, the results didn’t make sense.

That’s right, the shorter IL stay meant worse results. The jump is with WHIP and a small ERA increase for the short IL stays. All but the median ERA value are worse for the short versus long IL stay.

None of the medical people who I talked with could explain why this happened. If it was in-season, the results might make sense with the pitcher possibly coming back from the IL too soon. Maybe elbows need at least two months to fully heal, but if the pitcher comes back early they develop bad habits? I’m sure some narrative could make sense but it’s hard to find one.

I’m going to go with an approach I’ve always had, try to minimize my exposure to pitchers with elbow and shoulder injuries. Additionally, I’m going to completely say away from those with extended stays on the IL from shoulder injuries.