One of the facets of the human experience is the urge to compete, to defeat and take the spoils. However, with so many people needing to live together in a civilized way, we can’t just go loot the next city over, steal their cattle, and plunder their 401(k) accounts. So we developed two alternatives: “organized” war, and sports.
No matter how sanitized sports are, it’s important to remember that it’s still only a substitute for that animal urge to utterly crush the “other.” By defeating the “other,” people feel better about themselves, and by watching your hockey team defeat their hockey team, you can channel that aggression in a socially-acceptable way.
When the thin veneer between “organized sport” and “bloody violence” is crossed, though, it’s like that veneer never existed. The fight is the thing that thrills the spectators, although they are willing to watch a game of sport. :) When the fight happens, it’s beating the enemy literally as opposed to symbolically. It’s everything people want from a Viking raid or a scalping, but can’t really have anymore.
There’s a fine line between sport and violence. And just like other emotionally charged situations, it sometimes boils over.