From her 24th-floor apartment on 15th Street in Center City the night of March 20, Debi English, a retired nurse, witnessed the churn and chaos of the latest so-called flash mob and found herself yelling out into the darkness:
"What's going on, Philadelphia?"
Since then, the same question has preoccupied a weary city wrestling with the repeated spectacle of its young people running amok, lighted cell phones in hand, looking like contemporary rabble brandishing torches and terrorizing the countryside.
Overall, what has been happening here is not yet understood. City leaders and social workers are casting about for potential reasons for such unnerving behavior: Is it is the parents, the lack of school activities, poverty, the Internet?
Theories aside, what is known for certain is that teenagers met on South Street on March 20 - and in Center City on March 3, Feb. 16, and Dec. 18 - summoned via social networking.
"Come to South Street. South Street is poppin," beckoned the messages.
In each of the four incidents, violence broke out. In each, the teenagers involved were overwhelmingly African American males, although prosecutors say a significant number were girls.
"I think it's happening because these kids out there have nothing to do. It's happening out of boredom," said Marques Carson, 17, a student at Mastery Charter School in South Philadelphia. "They want to hang out and have fun, by any means necessary."
He attributed some of the violence and destructive behavior to the dynamics of large groups.
"When you're by yourself, you're one person," he said. "When you're with your friends you become another person. The peer pressure is on. . . . Too many kids are followers, not leaders."
"I think it just happens as a last-minute thing," he said of how these impromptu gatherings evolve. "Word spreads quick."
Yale sociologist Elijah Anderson, a part-time Philadelphia resident renowned for his analysis of African American culture here, is writing about the so-called flash mobs in a book to come out next year. The gatherings had a "quasi-carnival atmosphere," writes Anderson, calling them a "kind of social storm."
Many of the kids arrested in the Philadelphia incidents were from impoverished neighborhoods. A lot of them, Assistant District Attorney Angel Flores said in an interview, were having fun amid the mayhem. "They had smiles on their faces as they scared people at random," he said. "They thought that assaulting others was a form of enjoyment."
They were not on the hunt for particular victims, Flores said, although they trampled and punched people along the way - white, black, whomever - and damaged property. The biggest gathering was on South Street, where more than 2,000 people amassed, Flores said.
It would behoove us to figure it why this happened soon, said Darryl Coates, executive director of the Philadelphia Anti-Drug/Anti-Violence Network.
"We're going to be tested when summer comes," he said. "And we have to be sure we're ready as a city."
People have called these events flash mobs, but some say it's a misnomer, since flash mobs tend to be quirky, artistic gatherings organized on the Internet.
"I never heard of flash mobs that were violent," said Marilyn Moran, director of the Philadelphia chapter of the Social Media Club, an international group that promotes awareness of Twitter, Facebook, MySpace, and other social media. "These were pretty much riots."
Philadelphia appears to be leading this dubious trend. It's so new that the FBI, the American Psychological Association, and the Criminal Justice Program at the Harvard Kennedy School have no experts on "flash-mob violence."
Joe Smith, 52, a sales executive for a Swiss engineering company, said he knew the difference between "real" flash mobs and what happened on South Street on the first evening of spring.
In August 2009, Smith was on the 500 block of Rodman Street when he was suddenly surrounded by young white women in high heels, holding cell phones. "They told me it was a flash mob," he said.
On March 20, Smith, who lives 60 feet from South Street, experienced a very different sort of gathering. "About 100 people were stampeding at me and screaming, sounding happy, holding cell phones," he said.
"I was scared to death. Then I got knocked down and twisted my ankle."
But Smith, who is white, said the "mostly African American group" wasn't trying to hurt him. "They didn't intentionally knock me down," he said. "I don't think there was any racial component. I was in the wrong place at the wrong time."
A 32-year-old South Philadelphia auto-repair worker disagreed that race wasn't a factor last Saturday. The man, who asked for anonymity for fear of reprisals, said that at 11:30 p.m. March 20, he and his girlfriend were eating with a married couple at Bliss restaurant on South Broad Street, whose front windows open onto the street.
Suddenly, a "totally normal looking" black teenager hit the man's friend on the head three times, then ran off. The man followed, but soon gave up. As he returned to the restaurant, he heard other African American teens taunt him, saying, "What's the matter, white boy, you scared?" and "All the white people are scared" as they laughed.
Another person in Bliss at the time corroborated the account, for which no police report was filed. An Inquirer reporter who spent more than two hours on South Street observed one fight and some pushing and shoving, all involving black teenagers.
Anderson, the Yale sociologist whose specialty is urban inequality, said in an interview that he believed there was "pent-up frustration, even hostility" among young black people living alienated, isolated lives in "hyper-segregated, poor neighborhoods."
When they use texting or social networking to gather, said Anderson, who taught at the University of Pennsylvania for 30 years, they revel in their numbers and it "makes disenfranchised kids feel powerful."
"Young black males . . . become ever more defined as people to fear," Anderson writes in his yet to be released book. "The negative reputation of the 'iconic ghetto' becomes powerfully reinforced . . . as this large, unfathomable place that sprouts 'bad' people."
Mayor Nutter, who has taken an aggressive stance against these gatherings, attributed the violence to just a few "knuckleheaded" instigators.
His spokesman, Doug Oliver, added: "It's ridiculous to suggest that there's a racial motivation behind any of this activity."
John Rich, a physician and an expert on urban violence at the Drexel University School of Public Health, said it would be foolish to ascribe racist tendencies to the youths who did violence, when their unformed teenage brains might be more to blame.
"This is the way adolescents are," Rich said. "Doing unwise, risky things is what adolescents do." When youths gather in groups, he added, violence can easily flash.
Flores said that, among 30 young people in court recently for the violence from these gatherings, some had planned to meet to fight among themselves. But others had planned to simply dance.
None expressed the desire to attack white people, he said. "They knocked down a 70-year-old African American gentleman," Flores added. "Then they ran over him. You didn't feel any safer if you were African American and saw these kids running."
We should be careful "not to demonize African American kids," said Ray Jones, executive director of Philadelphia Safety Net, a nonprofit antiviolence group.
Generally speaking, many poor, black teens live in violent neighborhoods, where the fighting is black-on-black, he said.
"But they're mobile now and can gather," he said. "This is the latest trend." He added that a difficult background "does not excuse bad behavior."
He reminds, however, that Philadelphia has long been a violent town.
Philippe Bourgois, a Penn anthropologist, agreed. An expert on inner-city poverty and violence, Bourgois said that Philadelphia is a "city that expresses masculinity and toughness through violence."
He added: "We have a violent tradition. This is a city that breaks windows to express happiness when the Phillies win."
Overshadowed by the news about violent black youths was a second, unpublicized gathering in Rittenhouse Square on the same night as the South Street event, according to Khalif Dobson, 18, a senior at West Philadelphia High School. Dobson is a member of the Philadelphia Student Union and participates in roundtables with Public Citizens for Children and Youth.
About 100 African American teenagers met in the square without incident after reading about it on Facebook, Dobson said. Police said there was no record of any disturbance there that night.
"It was just a gathering of people," Dobson said.
Students and community activists say that, given city budget cuts, there aren't many activities for young people, and gatherings like the one on South Street might become more commonplace.
As the end of the school year approaches, it becomes a worry, given the social-media mobbing that's occurred.
Vigilance is what's called for, say city leaders, who encourage parents to keep a better eye on their children's phone and Internet usage for clues to planned gatherings.
"If they're going to a social happening, we have to ambush the event," Coates said, "and put protective measures into play at the event to control crowds and behaviors."
He added that parents and teachers, adult friends and community leaders must "pay attention to kids' conversations" to hear about potential gatherings.
It's wise to keep in mind that the everyday violence and abuse that many poor teenagers live with "depress them and keep them stressed," said Phil Harris, a criminal justice professor at Temple University. Quick fixes won't come easily.
"People should remember," said Dobson, the high school senior, quoting Martin Luther King: "The riot is the language of the unheard."