Sadly, yes, Legia's fans or rather hooligans are well known for causing havoc on the streets, especially when a derby or match with especially hated rival is coming, and that unfortunetly is the problem with many football teams' "fans" here. This problem is so big it happens also on non-football matches, just a few days ago hooligans from football clubs Ruch Chorzow and GKS Katowice fought with police near our Spodek Arena in Katowice, where martial arts competition took place. They fought using knifes, axes and even Molotov Cocktails.
They aren't arrested because, sadly there still is silent agreement for this kind of behaviour in our country. I don't want to create some sort of argument aout politics, but especially now with our current government they feel like they have nothing to fear as long as they pretend they are patriotic. The decisions of club boards and players are the problem too - in many cases they instead of trying to fight the hooligans they seem to be fine with them, even calling the normal fans "picnics", some people even say they have made deals with the pseudo-fans in many occasions. Plus the punishments are pretty low so they aren't scared.
Personally I dont think a Polish club should be allowed to play in European Competitions until we have the situation under control.