This article was reported and written by staff writers Christian Davenport, J. Freedom du Lac, Michael S. Rosenwald, Brigid Schulte, Ian Shapira, Annys Shin and Kevin Sieff.

Peering through his sunglasses, Spencer Johnson, the security guard at the McDonald's outside Verizon Center, monitors his post like a military commander awaiting insurgents.

From his stool facing Seventh Street NW, he sees clumps of teens purposely bump each other, hit each other, knock each other out. He sees young people steal sodas or tourists' wallets. "You know, it's pandemonium. It's ugly," Johnson says.

Gallery Place, Washington's newest retail and entertainment district, a product of the construction of a downtown sports arena and a decade-long boom, has become a meeting place that transcends the city's usual dividing lines. The Seventh Street corridor from Penn Quarter to Chinatown has attracted an unusually mixed crowd, a blend of races and ages, of urban dwellers, suburbanites and tourists, all drawn by the street's restaurants, bars, theaters and shops.

But recently, according to business owners, visitors and police, the night scene has grown increasingly tense. Large groups of teens clot the sidewalks, threaten passersby, and confront one another with harsh words and frequent fisticuffs.

Last Friday, Metro Transit Police say, dozens of youths were involved in a massive brawl. Although police remain vague about its details, the conflict spilled from the subway station onto a train, injuring four passengers, scaring scores of others and resulting in three arrests.

Every big city has a spot like this, where different races and walks of life come together in a chaotic but alluring stew. New York's Times Square is the classic example. In Washington, Georgetown and Adams Morgan have long attracted big crowds, there in part just to watch and be with each other. Such gathering spots inevitably develop tensions around crime and traffic issues. For Gallery Place, the street fights and clusters of teens that have become more common recently are growing pains -- a challenge to police, a frustration for business owners and a sign that the area is coming of age as an urban magnet.

The clusters of teenagers hanging outside the Gallery Place Station aren't gangs, police say, but some are members of looser, less hierarchical neighborhood crews.

Their misbehavior ranges from loud, obnoxious clowning to vandalism and muggings. In response, D.C. police officers who cover this piece of real estate, Police Service Area 101, have stepped up their presence. A patrol car, lights flashing, sits at Seventh and G streets. A police van stands outside the McDonald's. D.C. Housing Authority police stick close to a cluster of boys who hang outside the Gallery Place movie house. Increasingly, restaurants such as Clyde's and Ruby Tuesday hire security guards to cover their doorways.

The police cluster where kids do, such as on the National Portrait Gallery steps on Seventh Street. The steps are no random teen meeting place, police Lt. Eddie Fowler says, but an elevated lookout where young people can see who's coming and going. "It's like they're watching a game," Fowler says.

Why Gallery Place? Fowler isn't entirely sure but offers this theory: It's at the intersection of the Red and Green lines, allowing kids from all over to converge; there are hipster clothing stores; and there's the Regal theater, which became the city's main teen cineplex hangout after the movie houses at Union Station closed last fall.

At Gallery Place, the crowds especially swell on nights when there are games at Verizon Center. So watch your iPhone, the police say. "They'll rip it right off your ear," one officer says. (Police say there's a guy in Pentagon City who will buy them hot, no questions asked.)