7. Rangers vs. Celtic

Background
Glasgow, Scotland. One major Scottish city.

Rangers, Celtic. Two major Scottish soccer clubs, one city.

Catholicism and Protestantism. Two major religions, one city.

Relations between Catholics and Protestants are generally pretty shaky at the best of times, but when you add soccer to the equation, things are taken to a whole other level. In Glasgow, the two religious factions are each represented by their own soccer team. Celtic is the Catholic team and Rangers the Protestant. Let's just say that sometimes things can get out of hand.

Why This is a Great Rivalry
As if opposing soccer fans didn't dislike one another just on general principle, throw in religious hatred as well and you've got yourself a truly great rivalry. The fact that both teams play in the same city and are perennially competing with each other for the Scottish league title makes the Rangers-Celtic rivalry all the better. The "Old Firm Derby" as their games are called have got to be about the most highly secured matches in the world. Any match up where fans have a high likely hood of serious injury or death makes this list any day:

http://www.youtube.com/watch?v=86XNiQttRzs&mode=related&search=