The so called liberal media (AP in this case via NPR) informs us that police at Berkley were shown in video "pulling people from the steps and nudging others with batons." Watch the video which shows the nudging. Makes sense to Colbert. He comments here.
This is just one of dozens of videos you can watch of protestors getting assaulted. This is another difference between the Tea Party and OWS. OWS protestors get beaten without provocation routinely. Also arrested. Not so for the Tea Party.