The term "flash mob" often refers to sudden group protests or performances in public places organized in advance on social media. Police use the term for attacks by groups of youths they believe to have been coordinated through social media. 

An off-duty police detective and his wife were injured when they tried to stop a so-called "flash mob" attack by several Philadelphia youths, police said.

On the said incident, The juveniles hurt six people in all when they randomly assaulted diners and shoppers in Center City on Saturday night, according to police.

Witnesses said a group broke off from a larger crowd of teens on Saturday night and began attacking people, police said. One witness told WCAU-TV that at least three people were bleeding from their heads after the random assaults.

Police said the off-duty cop tried to arrest one of the teens who was attacking a 20-year-old man and a 21-year-old woman at 16th and Walnut streets. Several people began punching him from behind, and one of them punched his wife when she splashed water on the attackers, police said. 

The detective suffered an orbital fracture to his right eye, while the five other victims received treatment for minor injuries. According o the police report they had arrested a sixteen year old and still looking for a footage of the whole scenario for them to arrest the remaining unknown suspects. 

Police said they arrested four teens after as many as 150 of them attacked college students and punched a police horse in the mouth near Temple Oct. 21. Investigators believe the attack started with the "knockout game," which is a senseless contest to knock passersby unconscious.

There are also some witnesses who doesn't want to be named said that it was unprovoked. And that they did not say anything and that they just found themselves getting beat up.