Beautifully done. Break down the norms of having the fans shouting at a muddied "them," and possibly start some good long-lasting friendships. I also think that Recife's idea of having mothers of troublemakers, as was linked to [1] is also a pretty clever way of keeping things from getting out of hand. It is rather heartening to see new ways of enforcing civility that aren't based around the use of force.
Oh dear I can't see this ending well most country's teams that have "ultras" and high levels of violence - there is an underlying political and in some cases religious tradition gong back in some cases 100's of years.
Right, this is the first thing I thought. For your average-to-serious supporter this will stop them getting swept up in singing (for example) sectarian songs, but Ultras are probably not blessed with this sort of conscientiousness and rational thought.
[1] http://www.smh.com.au/sport/soccer/brazilian-soccer-club-dep...