Arthur: Troy Tulowitzki and the Brittle Bones Hypotheses

From SABR member Robert Arthur at Baseball Prospectus on August 7, 2014:

In a twist of stunning unpredictability, Troy Tulowitzki is injured. Like the year before, and the year before that, Tulo is spending some time on the 15-day disabled list, after missing a handful of games for sprains and strains earlier in the season. Troy’s annual trip breaks up what was easily (on a rate basis) the best season of his career.

A glance at Tulowitzki’s injury history reveals a voluminous catalog of the many ways baseball players can be hurt. This year, Tulowitzki suffered a hip flexor strain. Last year, Tulowitzki had broken ribs. The year before, a torn muscle which necessitated surgery. Other injuries on his record include maladies in his foot, ankle, and hand.

Tulo’s pattern of recurrent injury stands as an example of the idea that some players are just injury prone, that is to say more vulnerable or likely to be injured on account of some inherent characteristic. Tulowitzki is not alone in being accused of this weakness: others who have borne the label include Jose Reyes, Carlos Quentin, and all pitchers ever (except Mark Buehrle). We don’t just have anecdotal evidence for the existence of a “health” skill, however. Using some regressions, I showed before that a strong predictor of a player’s number of days lost due to injury was how much time he had missed due to injury in the previous three years. This result gives credence to the idea that there is variance in a player’s intrinsic probability of being injured.

Tulowitzki’s case attracted my attention because of the way his injuries are all distinct from each other. In successive years he’s managed to strain a muscle in his abdomen, break a bone in his torso, and tear a muscle in his groin. While there are perhaps commonalities to these injuries, it’s clear that it isn’t a single, lingering problem that’s dogged Tulowitzki. He’s earned his injury prone tag by being hurt in different ways.

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Originally published: August 7, 2014. Last Updated: August 7, 2014.