This has happened numerous times when people want to get into gigs for free, especially big events. Due to the nature of the anarchist movement in greece there is a confidence to do things like this. On a similar note a famous American "punk" band had to cancel their tour due to Greek anarchists attacking one venue in Athens. It was over the fact that the band (whose name I forget) had just played for the US troops in Iraq.
Raw
also seen it here http://caraivp.blogbill.com/









http://www.mychemicaltoilet.com/2007/06/it_may_rain_it_may.html
http://www.postchronicle.com/cgi-bin/artman/exec/view.cgi?archive=21&num=87534
http://blog.wired.com/sterling/2007/06/greek-anarchist.html
Anyone have any idea what this was about or is it just another case of em... dismantling hegemony from below... or something...