Black on White unprovoked attacks in Chicago -- read the article here.
Welcome to post-racial America. Mainly white men are being targeted. Other reports I've seen recently indicate that white, middle-aged, often overweight (hence the 'polar bear' designation) individuals are attacked for fun. These are not thieves or muggers. These are punks, often in groups, that punch unsuspecting people in the face or from behind. They look for people who are alone and unlikely to fight back. They are not looking for a fight. Four on one is not a fight; it's an invitation to a beat down.
They probably don't do this as much in Texas or Florida where concealed carry is a possibility.