Incidents like KPB? If after identifying and banning offenders, it persist. Closed door stadiums [or allow just wome and children], plus hefty fine. I guess it would be hard to define the amount, but something more than freaking £50-80k. Incidents like the Serbia u21 match? Fines of at least half a million Euro. Bans [starting at atleast half a season possibly even out for 5 years], some kind of relative community service programs should be created [if there arent any]. Its really tough to judge whats good enough and whats going overboard, but what they currently do is certainly not enough.