The only violence I've ever seen at games was before and after several Watford vs Luton matches, which have something of a history. There are those out there who are in it for the fights, but they tend to keep themselves to themselves and seek out like-mindless individuals. Other than above, I've never seen anything actually at a match beyond a few idiots being mouthy. Football has certainly cleaned up its act, on the whole, but there will always be pockets of idiocy.