If you think the Red Sox-Yankees or Vikings-Packers rivalries are intense (and they no doubt are), take a look at this pub brawl between Ireland and Poland supporters before their big match.  Are these two clubs rivals?  To be honest, it doesn't seem like it actually matters, because regardless, they're about to play one another, so that's all anyone needs to get shit going.  It would be nice to see this sort of devotion in the US.  Unless you own a pub, because that's gotta be expensive.