Physical Danger
So what if you're not on the field of play? You could still get conked on the noggin by a foul ball or run over by one of your own tight ends.
Or get so stressed out and excited by those last crucial seconds in the game that you give yourself a heart attack .
Or become so caught up in the high life associated with professional sports that you engage in behavior that could injure yourself or others.
The point is, your job is awfully rough considering that you aren't actually playing the game. Keep an ice pack handy, and maybe take up yoga for the ol' blood pressure. You'll be glad you did.