You know the routine: Somebody gets plunked on the arm by a fastball, the other side retaliates, and soon everybody comes running from the dugouts and bullpens to push and shove. What you may not know is that it's more common on hot days.
Our friends at NCBI ROFL dug up a paper
that studied the number of batters hit by pitches during games from 1986 to 1988. The researchers found a close relationship between increasing temperature and increasing numbers of plunked batters.
Perhaps the hot weather gets under pitchers' collars. Or, maybe by the time the dog days of summer roll around, teams have played one another enough times to get the bad blood going.