Hate to be the get off my lawn guy but out of thousands of thrown snowballs something is bound to hit a player in the eye, kinda like the freak accident when Jeff Tripplette hit Orlando Brown in the eye with a penalty flag. Then think of the liability if the league doesn't stop it. It's fun, but if you don't control it people start trying to outdo one another ("Bet I could hit THAT guy right in the f----in head! Watch this!") and something bad is bound to happen.