I spent last Christmas with family at my niece Julie's house.  In that it was a houseful of passionate Football fans, that was the topic of many of the conversations.  My great nephew Tommy, who doesn't care for any sports, asked an interesting question: "Why do you care if a team wins or not?" I sort of had an answer but couldn't really phrase it properly so I let it go.  I vaguely recall something I read a long time ago that made sense to me.  I'll be paraphrasing it.   
    War is deep in our Hairless Killer Chimp DNA.  Professional sports are a semi-civilized substitute for war.  They scratch the itch, usually without anyone getting killed or maimed, cities being razed, refugees fleeing for their lives, etc.  At first that might sound insane but think about it... you've got the army or team representing a particular city state, you've got the uniforms, the mock battle, fight songs, etc.  It makes sense to me.