Few years ago I could seriously compare it to England's hooliganism in 1980's but now I think it's not so extreme. I mean there is something that we call ustawka it's when fans of 2 clubs meet in for example forest or in field and they fight but it's for fans that are reffered as ultras but they do no harm to other people who just come to watch the game. And matches in our top league called Ekstraklasa are often peaceful, but there are few clubs that hate each other so much that they can riot. For example I come from city called Szczecin, our biggest club is Pogoń Szczecin and clubs that we hate the most and often fight are Lech Poznań, Wisła Kraków and Cracovia (just to be clear I don't fight, I'm not ultras). Maybe it's good than that we are in 2nd league still fighting for promotion. But I can assure you that if you came here for international match, you wouldn't get any trouble. Especially wearing Chelsea scarf or something like this because Chelsea has a lot of fans here in Poland.