I am sure football gangs have acted as a 'force multiplier' before for political protest, usually not for mass movements as in Egypt, but extreme right wing / nationalist groups in Russia and the UK for two examples.

In this instance were the Ultra's combat skills available when the confrontations with the riot police occurred or after they retreated?

When rioting emerges from public protest the presence of groups like the Ultras will make a dramatic difference, for their discipline, experience and sheer delight in fighting. Crowds may waver when the state responds to the start of a riot, at that moment the Ultras provide a shell of protection as the crowd decides what to do.