Holding teams responsible for their fans' behavior

In the Euro tournament, Russia got a suspended disqualification due to the violent behavior of Russian fans.

But I wonder just how much control Russia has over its fans, short of hiring its own police force to go about in the stadiums and control everyone.

Secondly, doesn’t this give incentive for false-flag attacks? Suppose someone wants to see England disqualified from a tournament - couldn’t they go about dressed up as English fans and commit acts of violence?

Do they have segregated seating for fans from different countries…depending on where you buy the ticket? I know some soccer stadiums try that. That may cut down on “false flag” attacks.

When you have several thousand people determined to create trouble, I don’t know how you can really control them. Threatening the team with punishment may be seen as a last result…if they really care about the team, they won’t do anything threatening.