For some reason, I'm fascinated by the concept of injury-proneness. Twice this season, Josh Hamilton was injured while running into walls. Intuitively, this is not evidence of proneness to injury. Milton Bradley pulls hamstrings while running bases. Intuitively, this is evidence of proneness to injury. What's the difference? Both activities occurred during games. One could say that both are occupational hazards.
The difference is this (or so I theorize). Injury-proneness is comparative. Read this. Two runners, engaged in the same activity; one gets injured; the other doesn't. The former is injury prone; the latter is not. It's pretty clear that anyone who ran into the walls that Hamilton ran into would have been injured at least as much as he was, so Hamilton's injuries were not due to, or rather, are not evidence of, injury-proneness. It's equally clear that only a couple of players out of 100 would pull hamstrings while running bases, so Bradley's injury is due to, or evidence of, injury-proneness.
My theory accounts for the data. I've seen no other theory that does.
Addendum: A person is injury prone, in my view, if and only if he or she gets injured while doing things that would not injure most others. The term "most others" is admittedly vague, but so is "injury prone." Since running into a wall as Hamilton did would injure most others, Hamilton's being injured while running into a wall does not constitute evidence of injury-proneness. Since running bases would not injure most others, Bradley's being injured while running bases constitutes evidence of injury-proneness.
Addendum 2: A synonym for "injury-prone" is "frail." You don't have to be frail to be injured by running into a wall, but you do have to be frail to be injured while running bases.
Keith Burgess-Jackson, J.D., Ph.D. 