Portugal was about to get wrecked.

It was the eve of the 2004 European Championships, an every-four-years soccer tournament that ranks second only to the World Cup in size and spectacle and that pits twenty-four of Europe’s top national teams against one another. Hundreds of thousands of fans were streaming toward sparkling venues across this sunny nation. For Portugal, this was a big moment, its coming-out party on the world sporting stage. There was just one problem, and it was the same problem that has shadowed European soccer for decades: English soccer hooligans.

The Portuguese organizers knew what they were up against because the previous championships, held four years before in Belgium, had provided a vivid lesson. The Belgian police had prepared well for the hooligans, spending millions training their force and equipping themselves with the best antiriot equipment, surveillance cameras, and information systems available. They had worked closely with the British government to identify and bar known troublemakers from entering the country. In short, they had been as ready as it was possible to be. And none of it had helped. Thousands of English hooligans, showing the sort of unified resolve their team has historically lacked, roamed wild, smashing shop windows, beating up bystanders, and battling phalanxes of riot police wielding batons, fire hoses, and tear gas. By tournament’s end, more than one thousand English supporters were arrested, tournament organizers considered banishing the English team from the tournament, and pundits were wondering whether international tournaments might be a thing of the past.

According to most social scientists, this reality was both logical and historically unavoidable, as English hooligans embodied the working-class aggression known as the English Disease. Decades of experience showed that the disease could not be cured, only its symptoms controlled. As the 2004 tournament approached, riots seemed inevitable. As one English writer put it, sunny Portugal was about to become the target of the “biggest English invasion since D-Day.” To prepare, the Portuguese government purchased $21 million of riot-control tools: water cannons, truncheons, pepper spray, and police dogs. It also looked at new approaches on controlling crowd violence—including the work of an obscure Liverpool University social psychologist named Clifford Stott.

Stott is a plainspoken, crew-cut man who specializes in crowd violence. He studied the Los Angeles riots of 1992 and the U.K. poll tax riots of 1990, and as the 2004 championships approached, he was working on a new theory of crowd violence that had less to do with the forces of social history than with social cues. His idea was that it was possible to stop the violence by changing the signals the police were transmitting. In his view, riot gear and armored cars were cues that activated hooligan behavior in fans who might otherwise behave normally. (Ninety-five percent of the people arrested for soccer violence, his research showed, had no prior history of disorderly conduct.) The key to policing riots, in his view, was to essentially stop policing riots.

Stott’s early trials of his model were sufficiently compelling, and the Portuguese authorities were sufficiently desperate, that Stott found himself, to his everlasting surprise, in charge of a high-stakes experiment: Could the most dangerous soccer hooligans in the world be stopped by a handful of social cues?

First, Stott set about training the Portuguese police. Rule number one was to keep all riot gear out of sight: no phalanxes of helmeted cops, no armored vehicles, no riot shields and batons. Instead, Stott trained a crew of liaison officers who wore light-blue vests instead of the customary yellow. These officers were trained not in riot control but in social skills: friendliness and ability to banter. Stott encouraged them to study up on the teams and fans and get good at making small talk about the coaches, on-field strategies, and team gossip. “We sought out people who had the gift of the gab,” he says, “who could throw their arm around someone and chat with them about anything.”

The bigger challenge for Stott was rewiring police instincts. The English hooligans had a habit of kicking soccer balls in public places, booting the ball high into the air and down onto the heads and café tables of bystanders, thus igniting the kind of small-scale confrontations of which riots are born. Conventional police procedure is to immediately and forcibly intervene and confiscate the ball before any open fighting breaks out. But on Stott’s advice, Portuguese officers were instructed to do something more difficult: to wait until the hooligans kicked the ball within reach of the police. Then and only then could the police take the ball and keep it.

“You have to play by the shared rules,” Stott says. “The police can’t just go take the ball, because that’s precisely the kind of disproportionate use of force that creates the problem. If you wait until the ball comes to you and simply hang on to it, the crowd sees it as legitimate.”

To some Portuguese police, Stott’s ideas sounded illogical if not insane. Several protested, saying that facing gangs of violent hooligans without protective armor was reckless. By the time the tournament arrived, the English press had derisively termed the program “Hug-A-Thug.” The sporting and scientific worlds waited doubtfully to see if Stott’s method would work.

It worked. More than one million fans visited the country over the three-week-long tournament, and in areas that used Stott’s approach, only one English fan was arrested. Observers recorded two thousand crowd-police interactions, of which only 0.4 percent qualified as disorderly. The only incidents of violence occurred in an area that was policed according to the old-fashioned helmet-and-shield system.

In the ensuing years, Stott’s approach has become the model for controlling sport-related violence in Europe and around the globe. One of the reasons it works is that it creates a high-purpose environment by delivering an unbroken array of consistent little signals. Every time an officer banters with a fan, every time a fan notices the lack of protective armor, a signal is sent: We are here to get along. Every time the police allow fans to keep kicking the ball, they reinforce that signal. By themselves, none of the signals would have mattered. Together they built a new story.

For Stott, the most revealing moment in Portugal came halfway through the tournament when a yellow-vested Portuguese policeman had an encounter with an overly exuberant English fan. The policeman tried to calm the fan; the fan resisted, and then the policeman reflexively used force, grabbing the fan roughly. A ripple of energy moved through the crowd; people shouted and pushed. It was exactly the kind of situation Stott feared most: a single overuse of force that could cause a disastrous spiral.

But that didn’t happen. Instead, the fans shouted out to one of the blue-vested liaison officers. “The fans called over to the liaison and said, ‘Hey, can you come and sort this policeman out for us?’” Stott says. “The roles had reversed, and the fans were policing the police. They had socially bonded with the liaisons. They saw them as their advocate.”