Video here. Based on the video, it looks like a single officer was arresting a protester when a crowd surrounded him and starting yelling to let the protester go. The protester being arrested went limp to make the officer drag him away, and then another protester ran over and knocked over the officer so the officer would let go of the protester being arrested. At first the officer responded with pepper spray to try to keep the angry mob away. But the crowd kept coming at him, so he let go of the person he was arresting and backed away to his squad car. The crowd then cheered their victory. Lovely.