That kind of stuff is quite common. you take Liverpool they have two teams "Everton"
which is catholic and "liverpool" which is protestant.and they have their counterparts in Scotland Rangers and Celtic....even in the army if you are protestant and from liverpool then you join a Scottish regiment....i don't really understand it myself , so I may be saying some of it wrong ( I tend to get along very well with people of ethnic minorities myself......coz I treat people how they treat me, If they are nice and polite then I am also, to me that is what defines a person..you can't pick racial origin, but you can choose to be polite..being polite is the cheapest thing..............it costs nothing.you don't need to shout about honour, if you behave honouraby then you get it back.
Sadly in soccer you see stuff like this, people who are tribalists and don't just love the game for it's great skill and artistry and just see it as one army facing another.but true sportsmen see it that way and will cheer for great skill such as in the late george best