In that case I think a firm warning to sort out their behaviour, followed by ejecting them if they don’t behave, is the way to deal with it on the day, although from what
@Martonmosser is saying some of them should have probably been refused entry based on dress code from the outset though.
I do agree with you about the groups though 100% as it’s a recipe for trouble. So as far as future policy goes, I think it’s probably best to not accept group bookings for away fans.
My main gripe was the idea of a complete blanket ban on anyone inviting an Away Guest, which I think is overkill.