The driver says, for no apparent reason they attacked his passenger at 15th and Chestnut on Saturday night.
"He didn't say anything. They said 'we need a cab,' and he said 'okay, I'm getting off. You can have the cab if you need it,'" said the cab driver, who did not want to be identified.
His passenger was Brian Goldman, a senior at the University of Pennsylvania, where he writes a weekly column for the student newspaper.
In his column on Monday, Goldman says his window was open and he was suddenly sucker punched in the face.
The cabbie says the teens were hurling racial insults at Goldman. The driver got out of the cab and managed to get a tire iron from the trunk to fend off the mob as Goldman ran off.
In his column, Goldman complains that dozens of bystanders did nothing, writing "I have never felt such discomfort, having people around witness violence and not come to your defense, or in this case, simply dial 911."
Goldman also never called the police.
The cabbie later flagged down police who returned to the scene and arrested three teenagers. They were laughing and mugging for the camera in the back of the squad car.
"They may have thought it was some kind of fun. It was not fun, it has serious implications and it does negatively impact our reputation," said Philadelphia Mayor Michael Nutter.
The attack comes on the heels of the beating death of 23 year old Kevin Kless. He was killed at 4th and Chestnut two weeks ago.
The police continue their investigation into this latest incident. The three suspects are charged with aggravated assault and may also be charged with a hate crime.
