Batter Injuries and Future Performance

Predicting hitter injuries has been a fool’s errand for me. Besides players with chronic injuries (e.g. Albert Pujols and Ryan Braun), others and myself have made little headway in the field. With few guidelines, many fantasy analysts and owners handle hitter injuries differently. Previously, I focused on a hitter’s recent injury history. This time I attempted a different approach and used the hitter’s career IL days. In the end, I found a useful and easy to remember injury threshold.

For the study, I examined hitters from the 2010 to 2018 seasons. I have IL data going back to 2002, so I hoped the preceding eight years of data would get most of the hitter’s 2010 career total. Additionally, I needed the next season (e.g. 2019) to compare results. Additionally, I set a minimum hitting threshold (100 PA) to include at least some semi-regulars. I know I may miss a hitter who is out the whole season, but the two-week callups were diluting the results. In all, I ended up with a sample of 2365 player seasons.

I had no idea where to start, so I split the hitters at 30-years-old and then bucketed them into 100 IL day bins.

The results for the over-30 crowd are nice and clean with gradual changes as the IL days increase. The year-to-year changes are almost twice as bad for the over 400 IL day group compared to the 100 to 199-day group.

As for the younger hitters, what a mess. The over 400 days can almost be ignored based on a small sample size. The average IL days are a rollercoaster up and down. There needs to be more bundling to find anything useful here.

I changed the threshold around a bit and found an ideal split to be around 280 accumulated IL days. I decided to round up to 300 days and here are the results.

I’m not surprised but the hitters under 30 are experiencing the same production decline and playing time reduction as their older counterparts. The 300-day threshold doesn’t discriminate. Once a player reaches the 300 game threshold, he is likely to at least spend at least some time on the IL.

Remember, the decline doesn’t start exactly at the 300 game threshold. Hitters in the 200 to 299 range are seeing their skills and playing time degrade at an increasing rate. There is always a grey area … always.

For reference, here are the hitters who have reached the 200 IL day threshold along with their age and average NFBC ADP (top-100 picks highlighted).

Most of these hitters have been declining for years and are being rostered late in drafts. Not all though. Four hitters are being taken in the top-100. Nelson Cruz was able to stay healthy once he became a full-time DH, so he’s been an exception to the general decline. Maybe Jorge Soler won’t decline since he’s primarily a DH now. Giancarlo Stanton and Tommy Pham are the two early picks who owners will be counting on for production and may end up with less than expected. Both need to be rostered at a discount.

Overall, I’m happy with the results. I have an actionable range and expected decline. With the drop being around three points of wRC+, an owner can drop the hitter’s prorated production by 3% across the board along with the playing time. The adjustment doesn’t mean the hitter is undraftable, they just need to come at a discount.

After diving back into the IL work, I saw a couple of other areas to improve on.

A one-off study that might work is weighting the recent seasons more than the others. I’m not sure what is the best method to approach the problem. I have too much on my plate right now (i.e. 2021 version of The Process) to just fart around making up numbers.

Another factor that I’m not able to take into account but I believe is important is surgeries. A hitter could have played through an injury, sat most of September (no IL needed), and then had offseason surgery. They would not be included in the preceding analysis. The problem is collecting the surgery information.

That’s it for now. I may come back to this topic soon but I want to take a stab at pitcher injuries again along and hopefully start prepping for the season’s start.