Congressional staffer Charlie Armstrong still laughs about the time armed guards escorted him from a soccer game in Chile.

It was 2005 and Armstrong, who works for the Senate Office of the Legislative Counsel, had flown to Santiago with a few friends to support the D.C. United. When they arrived at the stadium, the small band of black and red supporters found themselves facing off against 20,000 raging Chilean fans.

The match grew so heated that officials had to intervene, ushering Armstrong and his friends behind an 18-foot protective fence to shield them from the riled-up crowd. When the final whistle blew, guards again swooped in to safely remove the United fans from the scene.

It was an unusual experience. Typically, soccer fans on the Hill spend more time fighting indifference. In a town long known for its love of the other kind of football, the sport associated with minivan-driving moms and European hooligans is still something of a mystery.

Despite their small numbers — or maybe because of them — the capital’s soccer fans are a die-hard group.

On game day, otherwise normal District residents transform into flag-waving, beer-throwing, chant-screaming super fans. For members of the United’s two major supporters clubs — the Screaming Eagles and La Barra Brava — cheering for D.C. is more than just a way to pass an afternoon. It’s a full-time obsession.

Armstrong and friends Paul Callen and Noah Wofsy, who work in the House Office of the Legislative Counsel, bought their season tickets in 1999 and haven’t looked back since. The Congressional staffers weren’t even soccer fans before the United took root in the nation’s capital. 

“We just went to a game on a lark because it was a short walk to RFK,” Armstrong said.

The three have traveled across the country supporting the United, which is no easy feat for lawyers who have to meet the demands of a Congressional schedule. But the spot they keep coming back to is Section 231 in RFK Stadium. 

Long before their obsession with the United began — before the three bought season tickets, plane tickets and countless beers — the team’s appeal was very close to home. 

“Like many people in D.C., we come from different places, and we’re not natives of the area,” Wofsy said. “This was something we could feel would be ours and we wouldn’t have to share our loyalty with our hometown.”

And RFK Stadium’s location means getting to and from games — and tailgates — couldn’t be easier for those living and working on the Hill.

“On a beautiful spring evening, there’s nothing better than walking across Capitol Hill to RFK,” Armstrong said.

The team that has captivated Armstrong and his friends is considered the most successful club in Major League Soccer history with a record four MLS Cups, though it hasn’t done well recently. In the 2010 season, the United finished dead last in the league. This year, things are looking up thanks to a new head coach, United legend Ben Olsen, and a promising squad out on the pitch.

The fans, however, never thought of abandoning the black and red. A main reason, they said, are the supporters clubs. 

“I didn’t go in as a soccer fan, but I loved the enthusiasm,” Callen said.

Part social experience, part charity organization and part college kegger, these groups keep the United faithful connected with the team and Capitol Hill beyond the final whistle.

Since the Screaming Eagles’ inception in 1995, more than 4,000 people have signed up with the club, spokesman Kim Klyberg said. This season, 600 members are active and more people are joining and renewing every day. Guests are always welcome to buy a seat in The Nest to cheer along with the Screaming Eagles on game day, she added.

La Barra Brava counts 1,500 fans as members, and like the Screaming Eagles, it sells extra tickets in its designated section. The scene’s a little different in this zone, however. Beer rains from the sky, the seats don’t stop shaking and the songs and chants have a distinctly Latin flavor. 

Robert Gillespie, one of the group’s leaders, who are known as elders, said La Barra Brava found its inspiration with South American supporters clubs. Smoke bombs, streamers and cervezas are not just encouraged throughout the 90-minute match — they’re expected.

The group also hosts tailgates in Lot 8, just a short walk from the Screaming Eagles’ well-organized barbecue and microbrew pregame festivities. In Barra Brava territory, live bands offer the soundtrack to drinking contests, beanbag tosses and an array of food options.

“The great thing about our tailgate is we have a real sort of community spirit, and everybody contributes food and drinks,” Gillespie said.

And in the past five years, he noted, there’s been tremendous growth for the group, which counts federal judges, professors, construction workers and Hill staffers among its members.

“We socialize a lot on the Hill — on H Street and on Pennsylvania Avenue,” he said, adding that the Pour House is a popular Barra Brava spot. “We’re close by the folks who work on the Hill.”

At their core, though, the supporters clubs revolve around those 90 minutes when the ball is in play and the fans are screaming in the stands.

“When you go to other sporting events, whether it’s Nationals, Capitals or Wizards games, what do you get when you’re sitting in the stands? You get a constant barrage of PA announcements telling you when and what to cheer,” Wofsy said. “You go to a soccer game, and there’s none of that. All the noise that you encounter at a game — that is generated by the people in the stands themselves. The people in the stands made it happen, and I just love that.”

Of course, as Armstrong discovered in Santiago, sometimes matters can get a little out of hand when people in the stands take charge.

“We were in a section of the stadium separated from the rest of the crowd by an 18-foot fence so no one could get in there and beat the crap out of us,” Armstrong said. The D.C. team ended up losing the game, 3-2, but for Armstrong, it may have been for the best.

“If D.C United had won, we would have been jumped,” he said, laughing.

The D.C. United play the LA Galaxy at 7:30 p.m. Saturday. Tickets can be purchased through the Screaming Eagles, La Barra Brava or ticketmaster.com. To find out more about the United and its supporters clubs, visit dcunited.com, screaming-eagles.com and barra-brava.com.