I was just reading that every ticket sold for baseball games since 1913 have had a disclaimer on them for these cases. An easy arse cover. There's been some serious injuries over the years too, although I don't know if anyone's specs have ever been damaged.
“The holder assumes all risk and danger inherent to the game of Baseball, whether occurring prior to, during, or subsequent to, the actual playing of the game, including specifically (but not exclusively) the danger of being injured by thrown bats, fragments thereof, and thrown or batted balls, and agrees that the (name of club) are not liable for injuries resulting from such injuries.”