PHILADELPHIA (CBS) — On the same weekend that two men were beaten by violent mobs of teenagers in Center City spurring a police crackdown, another man now says he was randomly attacked on Kelly Drive.

Christopher Dean says he was biking along the drive around 6 p.m. on Sunday evening, July 31. It was a sunny day and plenty of people were out. He was between Boathouse Row and the Girard Avenue bridge heading west, he says, when he saw a group of four or five teenage boys standing by the side of the path. Suddenly, one of them stepped out toward his bicycle and punched him in the face.

Dean was hit so hard, he says he blacked out. Dean says the teens appeared to be between 15 and 18.

“It felt literally like a blunt force nose of an airplane smacking into me full force. I think it was as hard as he could possibly hit somebody,” Dean said. “You don’t know what’s hit you when something like that happens. It takes me three or four seconds probably to realize I’ve just been punched.”

Dean says he managed to pedal another hundred yards before he was helped by two people having a picnic. Pictures show his face bleeding profusely. He needed stitches and his skull was fractured in three places, he says.

“The doctors … said that’s brass knuckles, the only way your skin can be opened up that way, that’s brass knuckles,” he said.

Police confirmed Dean’s story and said there have been no arrests.

Dean’s incident happened just two days after two other violent attacks by teenagers in Center City. On Friday night, July 29, one man was beaten at Walnut and Juniper, and another man was attacked at 15th and Sansom.

Dean says he is speaking out now because he doesn’t believe the city is doing enough to combat the random violence.

On Monday, Mayor Nutter laid out a plan to prevent the so-called flash mobs, mostly by imposing a tougher curfew in Center City and University City on Friday and Saturday nights. The city is also keeping 20 recreation centers open later on those evenings to give kids something to do.

But none of that would have prevented Dean’s incident, which occurred early in the evening and outside the new curfew zone.

Dean says he believes the city needs to install more cameras, especially along Kelly Drive. Unless the violence is put in check, Dean says the biggest victim might be the city’s reputation.

“If they [tourists and visitors] get wind that this is a dangerous place, this city – generations of work to make this city what it is – and it is a gem of a city, is ruined,” he said.

Reported by Ben Simmoneau, CBS3