Using Curveball Spin to Predict Blisters

Pitching blisters were an afterthought just two years ago but the reported instances have jumped the past two seasons. Detailed accounts were written by Eno Sarris here at FanGraphs and Ben Lindbergh at the Ringer.

Throwing a curveball may be to blame according to Sarris:

But we can’t dismiss that chart completely. The players who have gone down with blister problems have thrown curves 14.9% of the time, far above the 10-11% baseball as a whole averaged over that timeframe. The players who ended up on the list more than once averaged 18.9% curveballs. Enough to say there’s some smoke here.

Here are curveballs rates for any pitcher mentioned at Pro Sports Transactions with a bister injury and their curveball usage.

Blisters are limited to just curveball pitchers but it is a larger percentage. These are only the reported instances of blisters but there are non-reported instances. These unknown blisters are even more important as it might point to a struggling pitcher such as Reynaldo Lopez.

I'm trying to figure out how Reynaldo Lopez's curve went from a plus grade (60) to 16% Swinging strikes in '16 to only 6% swinging strikes last year.

Cut its usage in half.

I wonder if he dealt with blisters (googled w/ no hits)

— Jeff Zimmerman (@jeffwzimmerman) November 29, 2017

Basically, Lopez quit throwing his best pitch from the previous season which had a 100+ rpm drop. He had the lower spin rate in his first major league start in August. He might have had the injury before reporting to the major league team. Without the minor league spin data, I decided to see if the spin changed on other reported instances and those can be related back to him.

The results weren’t as I expected them. Here is how the curveball changed for each instance.

What a result hodgepodge. After staring at them a little too hard, I came up the following general points on blisters and curve.

• Rpm levels change, up or down, before the injury.
• Pitchers throw fewer curves once hurt.
• Pitchers change their spin the season after an injury.

Basically, if some aspect changes, put up a red flag.

In the case of Lopez, I would bet the injury either happened at the end of 2016 and he adjusted his usage and spin for 2017 or it happen during 2017 while in the minors. I’m intrigued by how he’ll use his curve next season. According to previous prospect reports, it was his best breaking ball. Will he bring it back or just use it as a show-me pitch.

So what can fantasy owners take from this? Nothing predictive. But if a pitcher, who throws a curve, is struggling, investigate the curveball usage and spin. They could point to a pitcher dealing with an unreported blister. Also, if a blister has already been reported, owners may consider the pitcher’s curve nonexistent. For some pitchers, they may still be productive. For others, they may need to be benched.