Did you ever wonder why people are so passionately supportive of their favorite athletic team? It usually has something to do with support for their university or their city's professional team. But I believe it goes even further than that.
I believe it is a throw back to an era when humans moved in small, closely-related clans. Each clan had members who foraged for food and fought to protect the group. If your warriors defeated your neighbors' warriors, it meant your clan was superior.
Our athletic teams are our warriors. If you don't believe it, listen to the cheers: "Kill'em!" When we sit in the stands cheering, we are essentially watching our soldiers doing battle against the soldiers of the enemy tribe.
Come to think about it, maybe we take sports too seriously.