We may roll our eyes and shake our heads when opposing fans throw barbs (or rocks) at one another. It's just a game, we tell ourselves. It's really not that serious.
But honestly, who hasn't felt that powerful sense of pride when his college team wins, when his country earns a gold, when his hometown team brings back the big trophy?
And who, after his rival team lost a big game, hasn't Googled that rival's hometown newspaper to revel in the misery of opposing fans?
No, readers, for many it's not just a game.
And like any war, crossing enemy lines is risky.
Heading to the enemy's mother ship (read: stadium) without attempting to blend in (read: strip yourself of your team's jersey and cap), well, can be lethal.
Click on to see 10 stadiums which you should never wear an away jersey to.