I don't like that sort of sports rivalry crap. It's either dumb- supporters of Sunderland FC (on the North East coast of England), for example, have a rivalry with the fans of Newcastle United (further up the coast), which made no sense, as Newcastle have been in the Premier League (the first division) for decades, while Sunderland spend most of their time in the first division (the second division- weird, I know, but football's weird...), occasionally doing well enough to spend a season in the PL. So, the teams only played a game about once or twice every four years. That said, that is a particularly dumb example.
Or really dumb the way the Glasgow Celtic/Rangers rivalry ahs got tied into sectarianism and the Northern Irish conflict. The rivalry sort of makes sense- they're two teams in the same division, in the same city, but it gets taken too far. Most of the fans are fine, but, eventually, some idiots will take it too far. Of course, that applies to any team, group, nation, church or tribe. It seems to be human nature, unfortuanately....