Two women looked on, and when the attack was over, the whole group fled. The man suffered cuts to his head, face, and eyes, police said.
On Friday, police said the teenager had been charged with aggravated assault, criminal conspiracy, and related offenses.
Police spokeswoman Officer Tanya Little said officers had determined that the attack was an instance of the knockout game. The department is monitoring other assaults to see if they are linked to the "game," she said.
"The detectives are definitely taking a closer look to see if any assaults that come up could be a part of this," she said.
Friday night, a 25-year-old man told police he was knocked off a bicycle and beaten by a group of young people in South Philadelphia for no stated reason.
Police were called at 7:36 p.m. to 12th and Catharine Streets, where the man said he was knocked off his bicycle by two young women, said Capt. Laurence Nodiff, commander of South Detectives. When the cyclist asked why they knocked him down, three young men started punching him, Nodiff said.
Other area agencies have said they have seen similar incidents in recent months.
In Lower Merion, police said it was "possible" two attacks, in September and October, were related to the knockout game. Two 19-year-old men have been arrested in connection with the October attack, which targeted a 63-year-old man.
In Philadelphia, SEPTA transit police are investigating an October incident that appears to be linked to another phenomenon called "slap cam," in which perpetrators videotape each other slapping strangers.
In that incident, SEPTA spokesman Andrew Busch said, a man sitting on a train on the Market-Frankford Line on Oct. 26 was slapped on the side of the head by a juvenile while another filmed the assault. Busch said that assault was the only incident transit police have seen that resembled the knockout game.
Inquirer staff writer Robert Moran contributed to this article.