Oakland police and their support troops. Yes, rocks and bottles were thrown by protesters; I have already said their were violations on both sides.
But I wonder just how Yahoo News justifies this type of reporting, when all over the internet were onsite commentaries like this one. In fairness, it looks like the NYTimes basically rewrote the main stream media's press release as well. "Three police officers injured and one protester." I was three blocks away and saw over two dozen battered protesters receiving medical attention.
By the way if you want to feel the moment of conversion from a peaceful protester into a radical police hating revolutionary, read this post.