This footage was taken on Saturday, January 28th, by an Occupy Oaklander videographer who goes by the moniker Oheresy. I don't know exactly where or when, but it was most likely shot after the abortive attempt by Occupy Oakland marchers to take the Kaiser Convention Center as the police were pushing us back towards City Center.
Watch as an unknown man gets grabbed by two policeman for no apparent reason, is dragged and then beaten with multiple baton blows to his legs (four by a single officer, more by others). Or don't watch, if you tend to throw up.