Do groundball pitchers require Tommy John’s surgery more often?

So the other day, whilst podcasting with Mr McEwen, I made a statement outlining a rather shoddily-reasoned hypothesis I’ve had rolling around in my head for a while. When discussing the Clevelands pitching rotation/overall strategy which is to stack the roster with extreme groundball pitchers like Justin Masterson et al. (a strategy that they seem to be shying away from a bit now), I mentioned that I thought groundball pitchers tended to get hurt more than pitchers of a more neutral or flyball orientation.

Now, it should be said, I have absolutely zero evidence of this being the case and I said so. It’s just one of those things that feels true to me. This is rooted in the scant, yet still present evidence that pitchers who throw grip-intensive pitches (i.e. sinkers and sliders which tend to lead to higher groundball rates) get injured more often because said pitches and the pressure they put on elbows and shoulders.

But is there any real truth to it? The question is a difficult one to answer as finding any really reliable data on injury history is shoddy. There’s no single place to find sortable data on who has been injured and for how long.

Finding easily sortable data on shoulder injuries is impossible. I could go through every pitcher who’s pitched in the last three or four seasons Baseball Prospectus to match up groundball rates to instances of injury, but I would like to eat/sleep/work at some point in the next month, so that’s not happening.

Tommy John’s surgery, on the other hand, is tracked by MLB Depth Charts—at least since 2010, so it’s a fairly easy process to match up every pitcher who’s had Tommy John’s surgery to their groundball rate and see what the results are.

In order to establish what exactly we’re talking about when we talk about a ‘groundball pitcher’ I’ve consulted Rob Neyer who comes to the well reasoned conclusion that an ‘extreme groundball pitcher’ has groundball rates that consistently top 55%, while a regular-old ‘groundball pitcher’ consistently tops 50%. A flyball pitcher, on the other hand, can be considered any pitcher that has a groundball rate lower than 40%. Pitchers between 40%-50% are essentially neutral. Yes, these endpoints are arbitrary, but they’ll have to do for now and do a reasonable job of separating pitchers into rough types.

Since 2010, 9.0% of all pitchers with more than 100 innings pitched had groundball rates higher than 55%, 19.9% had groundball rates higher than 50% and 27.7% could be considered flyball pitchers with groundball rates lower than 40%. That leaves 52.4% of all pitchers with more or less neutral groundball rates. This passes the smell test.

Meanwhile, there were 91 players on MLB Depth Charts’ Tommy John’s surgery tracker since 2010—71 of those had minor or major league sample sizes large enough to determine what ‘type’ of pitcher they are. Here were the results when matched up to their groundball rates:

As you can see, not only was I wrong, it looks as though the opposite of what I thought is actually happening. Groundball pitchers tend to require Tommy John surgery less often than flyball pitchers when compared to their overall numbers. And the difference is statistically significant. Despite the fact that only 28% of all pitchers since 2010 were flyball pitchers, they represent 38% of all Tommy John surgery recipients in the same time frame. It also seems as though more ‘neutral’ pitchers fare the best in terms of avoiding major elbow injuries.

Of course, there are issues of sample size here. 71 pitchers aren’t enough to draw definitive conclusions, but it is enough to think there may be some sort of correlation here—it’s enough to ask further questions.

Let’s pretend for a second that 71 pitchers is statistically significant, what could some of the reasons be for this? Do flyball pitchers throw harder? Is there a pitch they use more often than other types of pitchers that may lead to more elbow injuries? These are questions I can’t really answer without a ton more research, but it seems like maybe there’s something here. How differing types of pitchers fare in terms of shoulder injuries would also be interesting if someone were willing to put in the time.

It’d be interesting to see someone from Baseball Prospectus do a more in-depth version of this since they have better access to the injury databases. What do you think?

Thanks to Steve McEwen for the average groundball rates and to FanGraphs, StatsCorner and MLB Depth Charts for everything else.