Well… Underworld didn’t play there. Sofar the news is that The Beasty Boys were on stage and about the end their concert when riots started on and around the festival grounds. ‘Anarchists’ set fire to cars etc…
pictures on a site in greek.

Online translation:
‘ Inconceivable finishing (before few hours) [bradias] that had the better conditions. Above that was [enthoysiasmenoi] from the organisation of Ejekt Festival and prepared [dithyramboys] for the two appearances of foreigner names, we were rolled up… And basically, we remembered in who country we live…‘
‘ Little before the appearance of Madness it began first traditional “[ntoy]” those who they waited for patiently their line. Afterwards, the battle with [eiselthontes] follow the did decision of (need? him we will learn tomorrow) is left free the space of entry – pray, however, in the hands those who they came in order to they cause villain. In this cases comes first the safety of big mass of world, conform. However: the absence of any element of control can deter from potential episodes, but it allowed the predominance of anarchy. From and afterwards the surrounding space was at some time dominated from [koykoyloforoys] and [kranoforoys] with [gklomp], that burned cars, threatened even the world that was in the toilets, chased even persons that simply had the vip [paso] (him we saw also this with our eyes!). Lack of culture?
Something bad and of this…‘

More here, again in a online translation.

There’s news from different sources now (non official sofar) that it was announced at the festival that Underworld weren’t going to play because one of the members got hurt during the attacks at the backstage area. 🙁 Let’s hope everybody is fine.

update 2
report by someone who was there
‘ so I wish those responsible for Underworld not playing lose their genitals in a weird accident.‘