It's about civic pride. "My town is greater than your town". As mis-guided and rabid as some fans can get, the riotous behavior is more a product of the large # of people in a small area, and then add alcohol. It happened at Michigan State, it's happened all over. It'll happen again, perhaps in Ann Arbor, who knows.
I spent 4 years in Nebraska, with season tickets to the Huskers games. The same "civic pride" abounds when playing Oklahoma. I then moved to Washington D.C. with Redskin tickets. The same applied to Redskins vs. Cowboys. I am a Steelers fan and have been to many Browns vs. Steelers games.
It's all the same with the exception of the Brown's fans being the most disturbed and disqusting in my witnessed opinion.
BTW. I spent 3 years living in Michigan ( da U.P.), but I attended, and graduated from, The Ohio State University.