Football is, in a way, a thing of its own, but this is the sort of thing I've seen:
In our village, if say, England were playing Argentina, there would be an Argentinian flag flying outside the local pub. I dunno, it just feels a bit vindictive. By all means, don't actively support England, ignore the match or whatever, but what is fuelling the desire to fly the opponent's flag? It's a way of saying 'fuck you, English' and to any English living here, it feels unwelcoming [understatement].
By way of contrast, if England doesn't qualify for a big tournament (increasingly common), they tend to go, ah fuck it, who's the nearest to us, we'll support them, and go with Scotland, or Ireland, or whoever.
There just feels like a simmering resentment. Not from everyone, certainly, but from more than just an extreme minority.