I'm sorry if (IF) that fan was acting like a twit leading up to that (we really don't know the extent to which he was causing aggro do we?) then he probably deserved a biff on the head.
Thing about footie fans sometimes. We love to dish it out but hate the idea of the fuzz dishing a bit out back at us.
All that said. Jury's out. I'm no fan of the police but I'm also not so much a snowflake to whine about the time when the cops got heavy handed with me when I was being a mouthy shit.