I've selected one of many livestream videos of the daylong confrontation to illustrate what really happened. I picked this one because it shows a wider spectrum of events, including incidents where some of the protesters were definitely committing acts of violence. I think the overall contrast between the two sides speaks for itself.
Past violence by the Oakland Police Department and its allies have resulted in a situation of intense distrust and escalating confrontation. While I do not support the actions of the Black Bloc within Occupy Oakland because they are not committed to nonviolent struggle, there is still no comparison between the actions of the protesters and the actions of the police. The police are professionals, trained in resolving and de-escalating conflict. The protesters are just ordinary people improvising under pressure. So why is it that the actions of the police have been marked by deliberate brutality, while those of the vast majority of protesters have been relatively restrained?
Look at the video and decide for yourself. Setting aside any prejudice toward thinking of the police as the “good guys” (which the Oakland police most certainly are not), if you just think of these as two opposing groups, who is responsible for the violence you're looking at? I think any fair-minded person would come to the same conclusion.