D.C. United supporters’ groups such as Barra Brava, above, show 100 percent devotion to their squad. (Tony Quinn)

D.C. United’s playoff game had been postponed, a casualty of a snow-producing nor’easter in the New York area, but soccer’s ritual of thanking fans for their support needed to be respected. In the Red Bull Arena locker room, Coach Ben Olsen addressed a team steamed about MLS’s decision to delay another day.

“Do me a favor,” he said, “and get back out there and show them the appreciation they deserve.”

What happened next on that frosty evening 11 days ago exemplified the deep bond between United and its followers and the unique, unwritten oath between soccer players worldwide and their most loyal fans.

United’s players marched toward the north end and, peering to the upper deck through a swirl of flurries, applauded 700 fans who had bused up the New Jersey Turnpike in treacherous conditions to witness the club’s first postseason road game in five years.

Many of the players, as well as general partner Will Chang, then took the custom one step further by climbing over a retaining wall and up slippery stairs – “cleats and all,” midfielder Chris Pontius said — to join the devotees for solidarity and song.

“People might think it’s strange, but for us, it’s normal,” defender Brandon McDonald said. “It was like going to hang out with friends. Supporting us in those conditions, it’s the least we could do.”

The relationship continued the next day for a 1-0 victory, albeit with a smaller number of fans, and again last weekend in Houston, where United lost to the Dynamo, 3-1, in the first leg of their Eastern Conference final. Facing elimination against Houston at 4 p.m. Sunday, United will embrace the support of its unwavering followers among the close to 20,000 expected at RFK Stadium.

Organizers of the fan groups – Screaming Eagles, Barra Brava, La Norte and District Ultras — are planning a display of flags and banners unseen before in a setting that is always colorful and festive.

“It’s a special relationship,” Olsen said. “The day you arrive as a player, you begin to understand. It’s like we’re in this together.”

The connection between athlete and fan in soccer is unlike any other sport. You wouldn’t see Stephen Strasburg watching from the bleachers at Nationals Park if he’s not starting that day or Alex Ovechkin in the 400 level at Verizon Center while recovering from injury.

But many times over the years, United players not in uniform have joined the supporters’ groups on the rowdy lower east end of RFK. As far as anyone can recall, the first time it occurred on the road was in 2005 when midfielder Christian Gomez, serving a yellow card suspension, arrived unannounced in the pack of D.C. supporters at Giants Stadium and began pounding on a fan’s drum.

“That is what endears us to them,” said Jimi Butler, 38, a middle school teacher in Prince George’s County who oversees road trips for the Screaming Eagles.

Until 2004 or so, “I hated soccer. I had 100 percent zero interest in it,” Butler said.

But after touring Old Trafford, Manchester United’s historic stadium, and watching England’s national team in a tense British pub, “I thought to myself, ‘Oh my God, I see it. I get it.’ ”

Butler attended his first United match soon thereafter and was drawn in by the culture of supporters’ groups: tailgating before matches, the 90-minute chorus amid flags and banners during them, team-sponsored functions and the road trips.

“I don’t know if a team and a fan base could be closer,” said Paul Sotoudeh, a season ticket holder since 1997 and former Screaming Eagles president. “There is a real desire to have a presence at every away game, so the players know our hearts and spirits are with them.”

Eleven buses carried supporters to New Jersey for the second leg of the conference semifinals. While locals still recovering from Hurricane Sandy the previous week stayed away, United supporters turned the 25,000-seat Red Bull Arena into its private opera hall.

Given the grand effort they had made to attend the match, MLS’s decision to postpone did not go over well. United President Kevin Payne had gone to the upper deck to explain the situation when the players appeared on the field to show appreciation for the frigid followers.

“We don’t force guys to do stuff, but we certainly create an environment where they want to do it,” said Payne, who has overseen the club since its inception in 1996. “We don’t want our players to be isolated and living in bubbles.”

When the supporters realized the players were going to thank them personally, “All the negativity [about the game being postponed] was gone,” Butler said. “Fans were saying, ‘Thanks for respecting us.’ That was one of the classiest moves I’ve ever seen in sports.”

The buses returned to Washington, but the next day, about 300 fans traveled back to New Jersey. When Nick DeLeon scored the winning goal, he and his teammates pointed to the fans perched high above the targeted net.

Three days later, about 50 supporters attended the first game of the Houston series. Most were from Washington, but the group also included defender Daniel Woolard’s family, midfielder Perry Kitchen’s father and DeLeon’s relatives. They could have accepted complimentary seats and watched in a reserved area elsewhere but chose to join D.C.’s supporters.

The player-fan attachment in soccer can be traced to a dynamic that has existed around the world for decades. Fans have helped create clubs and served in influential roles in decision-making.

FC Barcelona, for example, has “socios,” who are eligible to vote on club matters, and “penyes,” fan groups recognized by the team. MLS’s Seattle Sounders allow season ticket holders and members of a fan alliance to vote every four years on whether to retain the team’s general manager.

United makes its own front-office decisions, but is in regular contact with the supporters’ groups to coordinate events and travel. Players have become friends with fans and work with them on charitable projects beyond the team’s community outreach requirements.

The bond between United’s players and fans can be explained through shared identity.

In a league that has emphasized slow growth through modest spending, some young players earn salaries comparable to the supporters’ and, like many in the groups, they need roommates to make ends meet in an expensive city.

The roster and fan base also share diversity along racial and ethnic lines. Former United stars Marco Etchverry and Jaime Moreno drew comfort from United supporters who shared their Bolivian roots.

A few years ago, in an effort to energize the Verizon Center crowd, United and the Washington Capitals arranged for D.C. fans to attend an NHL game en masse. The continuous standing and singing, however, didn’t translate to the hockey crowd.

“It’s been so ingrained in me, I don’t think the interaction between our players and fans is out of the ordinary,” said Olsen, a United player from 1998 to 2009. “When you compare it to the NBA, they don’t clap for their fans at the end of the game. But the NBA fans aren’t performing either. Soccer fans are performing.”

Win or lose, when United’s players applaud the supporters, “It’s almost as if we are saying, ‘Not only do we appreciate you coming and spending your hard-earned money, but we also enjoyed the show,’ ” Olsen added. “They are absolutely part of the show and it makes our sport and RFK unique.”