This happens here as well. It is par for the course actually and, more often than not, it is, in fact, staged so that the normal protestors will disperse, while the police and the “rioters” will perform their show, burn down some stuff, tear-gas the whole place and then, huzzah! success, every normal person is back home and afraid to take part in a peaceful protest.
The message is clear. Stay home or else…
This is a “dance” that we understand here and some of the political parties that participate in protests (mainly the Communist Party of Greece) have actually organised their own squads in a police-like fashion in order to guard the protest and push out the “violent elements” that try to ruin the whole thing and when they fail they rightfully and vociferously deny any involvement and are 100% against all violence and blame the “provocators”.
And that makes sense. Distancing yourself from violence is, I think most people would agree, the most reasonable political stance.
However things seem to be done differently in the USA, which always makes the news from over there interesting. E.g. I saw someone the phrase that they were “just a bunch of people having fun watching cars burn”… 
… and I was like, this can’t be real, but it was:
Why would anyone see all that and pretend that it is ok?
Very odd, politically.
So, while I do not know what’s going on there and I wouldn’t venture a guess, I have to say that this year there has never been a dull moment without pop-corn this year, and that’s for sure. Kind of makes you see why the “may you live in interesting times” was considered as such a dire curse. 
Ours does, practically. They have hired thousands of additional police officers in the past years. We might not have money for anything else, but for buying military weapons, frigates and hiring more police-officers our government always finds the funds. 
