You're in the boat...

youtube.com/watch?v=VCDZ-xYQNiU

That Irish fan trying to stop the fighting with beer in his hand at 0:39

if i ever travel to Europe, do i have to avoid cities with soccer matches playing?

yes

just avoid the stadium

Worry more about the obscene amount of pickpockets.

Watch out for muslims wearing extremely oversized coats

interesting.. do people in London not leave their homes if there is a soccer game?

the people in OP's pic aren't in a stadium. seems like anywhere close to a bar is unsafe

i have heard that about some cities

They are British.
Being worthless subhumans is just a part of their DNA.

Well ive lived in Britain 25 years and never had a problem running into football hooligans.

>be european
>never been pickpocketed in my life

just don't look like a an elderly Florida tourist and don't leave your shit lying around and you're good