I am NOT defending the cops here, but remember, this "wearechange" group are pasting snippets of videos online of things happening. We don't know what happened prior to this clip.
That said, I have seen a lot of videos and the cops are reacting poorly....but then, these people are intentionally antagonizing the situation in order to get a violent reaction.
Trust me, this isn't going to end peacefully. Once these people figure out that they are starting to outnumber the cops by a significant ratio, we're going to see Greece-like violence.