No one expected that the United States rugby team would win a second-straight Olympic gold medal, at the 1924 Paris Games, nor that prouder, more traditional rugby nations might have to wait 92 years for a chance to dethrone the American upstarts. A year after the U.S. upset favored France 17-3 in the Olympic final, the 23rd International Olympic Committee Session in Prague took away rugby’s Olympic status.

A quirk of college football history explains why the U.S. team was even in Paris. Following an injury crisis in 1905, schools in California temporarily switched from football to rugby, and spurred the sport’s growth on the West Coast—all but a handful of the players on the 1920 and ’24 teams were from California. And a lack of interest and a lack of sportsmanship explains why rugby was dropped from the Olympics. No more than three teams had competed at any of the four Games that had featured rugby (Paris 1900, London ’08, Antwerp ’20, and Paris ’24) and the recent Games in the French capital had been marred by crowd trouble.

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Over the next eight decades occasional efforts were made to revive Olympic rugby. Italy argued for its reinstatement for Rome 1960, the Soviet Union tried again for Moscow ’80, and South Korea, backed by the International Rugby Football Board, made another push ahead of Seoul in ’88. Signs of progress finally appeared in the mid ’90s. The IOC added the IRB to its list of Recognized International Federations in ’95, and wheelchair rugby, aka murderball, was included in the 1996 Atlanta Paralympic Games. When baseball and softball were dropped from the list of sports for London 2012, two holes were left in the Games’ schedule. But though rugby was put forward as a potential replacement, the IOC failed to reach an agreement on which sports to add at its 117th Session in Singapore in ’05. Four years later at the 121st IOC Session in Copenhagen, rugby was finally given the green light for the 2016 Rio Olympics.

Legend has it that back in 1823, during a game of soccer, William Webb Ellis, a student at an elite private school in Rugby, England, picked up the ball and ran with it. While children at less prestigious institutions might have been admonished for a clear violation of the rules, Ellis’s infraction led instead to the birth of a new sport. Ellis’s mark on the game was sealed when the official trophy of the rugby world cup was named after him in 1987.

Nowadays, rugby comes in a surprising variety of formats—technically American, Canadian, and even Aussie rules football are offshoots of rugby—but the most popular of these, and the type that will be played at the world cup in England this fall, is rugby union. When rugby was last in the Olympic Games, in 1924, it was rugby union, in which there are 15 players on each team, too. At Rio, however, rugby union will be substituted by a variant called rugby sevens.

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​Sevens is played on exactly the same size field as the full version of the game, but, as the name suggests, only seven players per team and with just two seven-minute periods (and a one-minute break at halftime). The effect of stripping out so many bodies is to open and speed the play up significantly. The football analogy might be street football, where teams are trimmed down to just a handful of players. Sure, you still have a quarterback, but other personnel have to play a wider range of roles, and there’s no way you can afford to put five men on the line.

Beyond the limit on personnel and time, though, sevens is still identifiably rugby union. The ball can only be passed laterally or backward, or kicked forward. When the ball goes out of play on the sidelines, the game is restarted with a throw-in called a line out, and when the ball is knocked or passed forward, play restarts with a scrum. Points are scored with tries (five points), where a player touches the ball down in the opposition’s in-goal area at the end of the field, conversions (two points), which are place kicks through the goalposts after tries, and penalty kicks or drop kicks (three points).

If rugby is English, sevens is Scottish. In 1883, two butchers from Melrose, Scotland, dreamed it up as a fund-raising event for their local rugby club. The game caught on nearby, but spread slowly elsewhere: the first sevens tournament outside of Scotland wasn’t played until 1921, and the first official international tournament didn’t take place until 1973. In keeping with tradition, the trophy of the sevens world cup tournament, first played in 1993, is called the Melrose Cup.

Construction in April at Deodoro Olympic Park, which will host several sports during the Rio 2016 Olympics Games. Buda Mendes/Getty Images

All of the games in the rugby tournaments at Rio will be played in the 15,000-seat Deodoro stadium in the west of the city. Since each contest lasts just 15 minutes, squeezing multiple games into the daily schedule is simple. Both the men’s and women’s competitions will employ exactly the same formats, the women playing from Aug. 6 through Aug. 8, and then the men playing Aug. 9 through Aug. 11. There will be 12 teams split into three groups of four, and group-stage games will be played over the first day and a half. Eight teams will advance to the knockout phase from the three pools—the first and second place teams, plus the best two third-place teams. Quarterfinals will be played on the afternoon of the second day, semifinals the morning of the third, and then the medal rounds later that afternoon.

Brazil, as host nation, gets an automatic entry. For the other teams, the first way to qualify for Rio was coming top four in the 2014-15 Sevens World Series. On the men’s side, Fiji, South Africa, New Zealand, and Great Britain (via England’s success) got in that way, and on the women’s, New Zealand, Canada, Australia, and Great Britain (England, again) did the same. The next route in is by winning one of the six regional tournaments—three more men’s and women’s teams have already qualified this way, with three more tournaments to play this fall—and the remaining spot will be handed out at a final qualification tournament to be scheduled sometime next year.

Big names still missing from the list for Rio include Australia and Samoa’s men’s teams, and Russia’s women’s squad. Russia was edged out by France at the European Women’s Sevens Championship in June, and now must wait to try to win that very last spot in 2016. Australia and Samoa will both be hoping to secure qualification at the Oceania Men’s Sevens Championships this November, but two into one won’t go and at least one of them will need to count on next year’s repechage.

In general, rugby sevens offers a much deeper pool of teams than 15-a-side rugby union. Big rugby nations like New Zealand and England are still well represented, but the draw of the more lucrative full-size game can weaken their men’s sevens teams, and the need for less personnel allows others to more easily field a competitive team. The men’s rugby world cups are a great example of this. Though New Zealand and England each have the same number of titles in 15s as they have in sevens, two and one, respectively, Fiji, which has never gone further than the quarterfinal stage in the main world cup, ties the Kiwis with two titles in sevens. And from 2010 until last year, Ireland, ranked No. 3 in the world in 15s, didn’t even have a sevens team.

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However, the attraction of winning an Olympic gold medal, or even simply just being part of the Games, could draw players back to sevens. All Black center—and undefeated heavyweight boxer—Sonny Bill Williams is planning to win the world cup this fall, then switch to the sevens team and train for Brazil. Wallabies fly-half Quade Cooper turned down a lucrative deal with French club team Toulon to do the same. The challenge for those players who want to succeed at both 15s and sevens, though, appears exhausting. The men’s sevens tournament at Rio 2016 will come just nine months after the rugby union world cup, and then, after a year’s break, the cycle repeats with the USA 2018 Sevens World Cup, Japan 2019 World Cup and Tokyo 2020.

The Canadian women’s team stands out because, in contrast to the men’s team, it will be a favorite in Brazil. While the Canadian men are unlikely to make much of an impact at the world cup this fall, and are almost guaranteed not to be in Rio, the women came second in both the 2013 Sevens World Cup and ’14 World Cup. Having been identified by the Canadian Olympic Committee as one of its country’s best chances for a podium finish, the women’s team receives $1.3 million per year in funding.

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One intriguing factor in the Olympic Games will be the fate of the British teams. The politics of international rugby mean that England, Scotland, and Wales usually play as separate countries, and that Northern Ireland plays with the Republic of Ireland in a unified team. But at the Olympics, English, Scottish, and Welsh players face being condensed into men’s and women’s unified British teams. The Irish Rugby Football Union, meanwhile, has banned Northern Irish stars from joining in with the rest of the United Kingdom. If Ireland fails to qualify, though, some may be tempted to challenge that rule.

Other countries might breathe a sigh of relief knowing there is no risk of facing multiple British teams, unless, of course, they’re drawn against these super teams—the men will comprise the best from No. 4 England, No. 7 Scotland, and No. 12 Wales, and though the Scottish and Welsh women don’t play in the top-ranked World Series, a combined team will still include No. 4 England.

The good news for American fans is that there is a realistic possibility that both the men’s and women’s teams could reach the podium. Both have already qualified, and both are riding high on recent results. “Our women won the bronze in the last world cup, and our men just won the London Sevens,” says Alex Magleby, director of performance for USA Rugby, and a former captain of the U.S. men’s sevens team. “There’s no reason to think that we can’t continue to accelerate our growth, and by 2016 August be in that top three, if not top one.”

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Even if the Eagles lose their almost century long grasp on the Olympic crown, rugby is beginning to flourish again in the United States. According to the National Federation of State High School Associations, the number of high school boys playing rugby doubled between 2008–09 and 2013–14 and the number of girls tripled—though the totals, 1,440 and 322, respectively, are still dwarfed by other sports. At the collegiate level there are now 168 DI-A and DI-AA men’s teams and 87 DI women’s teams. “It’s cheap, there are no real barriers to entry, it’s a much, much safer alternative for boys than American football,” Magleby explains of the growth, and “it’s the only real contact sport for women.”

Many of the U.S. players are still crossovers from other sports, however. On the women’s team, for example, prop Kelly Griffin played basketball and soccer before picking up rugby her freshman year at UCLA, wing/fullback Lauren Doyle was a four-sport athlete at Meridian High in Macon, Ill., then discovered rugby the summer before her senior year, and prop Ida Bernstein ran track and played soccer at Syracuse before joining the rugby team. Bernstein also narrowly missed out on a place at Sochi 2014, as she tried to balance commitments in rugby, grad school, and bobsled. On the men’s team there are several converts from football. Wing Perry Baker spent two years with the Arena Football League’s Pittsburgh Power, and fellow wing Carlin Isles—who runs the 100 meters in 10.13 seconds—played as a receiver on special teams at Ashland University and practiced with the Detroit Lions. In contrast, captain and scrum half Madison Hughes, born and raised in London, grew up playing rugby.

Regardless of where any of them came from, though, according to Magleby, the Eagles’ aim for Rio is simple: “Gold medal, both teams.”