They're known as "flash mobs" — gatherings of people who use social media and text messages to stage a spontaneous group "dance-in" at a train station or get a big crowd together to imitate statues in a park.
The idea seems innocent enough, but in Philadelphia, flash mobs have turned violent and police are cracking down.
Pizza shop owner Joey Rocco has seen an out-of-control flash mob firsthand. His pizza place is on South Street, which runs through the heart of the city and is a popular hangout for both kids and tourists.
Two weeks ago, Rocco was finally getting some decent business after a long, snow-packed winter.
"Saturday night we had the windows open; it was a beautiful night," he says. "People were sitting in the window areas, and I just happened to look out and said 'Wow, the street is really crowded.'"
Some say the crowd of youths was in the hundreds. Others say thousands. Rocco says the kids began to jump up and down, and then utter chaos broke out. He says some of the teens started beating each other up, while others began banging on the windows of his shop.
"They were trying to climb in the windows on top of the people who were dining, so we pushed them out, we closed the doors and we locked the front doors," he says. "Whatever they had in mind, to me, it was like a home invasion."
Parents Called Out As Police Step Up
I ran for mayor, I didn't run for mother. So, I can't take care of everybody's child.
It wasn't the first violent flash mob for Philadelphia this year. In two other incidents, kids pushed down pedestrians outside City Hall and poured into the Macy's department store, where they tore merchandise off the shelves.
Of the 30 kids picked up and charged in those earlier incidents, 29 were hit with felony convictions.
After the third incident, Mayor Michael Nutter stood with a phalanx of police near South Street and warned parents to get better control of their children — or face charges of their own.
"Parents have a responsibility here, so we will do all that we can. I ran for mayor, I didn't run for mother," he announced. "I can't take care of everybody's child."
Nutter says he will make the city's curfew earlier if the flash mobs continue. One state lawmaker wants to bring back the mounted patrols. Police have created a special rapid response force.
Merchants, parents and police are scratching their heads trying to explain the explosion of violent flash mobs. The city's new district attorney, Seth Williams, says it comes down to the proliferation of computers and cell phones.
"Before, it was just you tell someone to meet you somewhere — if there was a fight you meet them at the school yard," Williams says. "Well now, instead of just 10 or 20 kids at most knowing about something, now you have 1,000 kids showing up at an intersection. And that's a problem that we as law enforcement have to try to deal with."
Just A 'Night Of Fun'
Benjamin Hamilton, 15, says he's never participated in a flash mob, but he knows kids who have.
"They talk about it like it's a game, or like it's just a night of fun," Hamilton says. "And really it's not, because it's really affecting people in ways they can't imagine. They might be affecting somebody that might get injured, or hurt, or emotionally hurt."
Hamilton says kids he knows dismiss the crackdown and the stiffer curfew.
Some teens did speak out on a local radio show about the incidents. But after one was targeted as a snitch, he was too afraid to speak.
The kids said the flash mobs were organized by "party groups." Some speculated that gang members took advantage of chaos.
It's been more than a week since the most recent violent flash mob sprung up, but police are concerned about this weekend, when temperatures are expected to be in the 70s.
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