Rugby is returning to the Olympics for the first time in 92 years, bringing the ruck, the maul and the hooker back into the lexicon of the Summer Games.
The format has changed, considerably, since the United States won the last rugby union Olympic gold medal in 1924. The abbreviated seven-player version was favored for Rio over the traditional 15-a-side game, and Fiji is favored for a breakthrough triumph. The aim remains the same: score more tries - grounding the ball in the opponent's in-goal area - and you're a good chance of winning.
It's fast and physical, with more emphasis on speed and passing the ball (always backward) than heavy contact.
Here's some things to watch in Rio, where the women's tournament runs Aug. 6-8 and the men's from Aug. 9-11 at the Deodoro Stadium:
Fiji has never won an Olympic medal, but it has never had a chance to play its national sport at the Summer Games. The world series champions are favorites in the men's competition, and expectations are high in the Pacific.
Englishman Ben Ryan took a squad containing an abundance of players with size, speed and natural flair for rugby sevens, and added extra discipline to every facet of the preparation from diet to drills. The result is a still entertaining, but more consistent Fiji team.
''It's the national sport, so our best athletes play rugby,'' Ryan says. ''We have been successful at it and that's also created this aura around the team, the way we play, totally different to every other side in the world. It's a risky, entertaining, exciting, slightly laid back - sometimes - way of playing the game. And we are doing it to a very high level.''
Sonny Bill Williams is a high-profile game hopper who will feature for New Zealand in Rio, another notch in a career that has involved switching back and forth from rugby league to rugby union to win some of the biggest prizes in those sports. Already a World Cup winner with the famous All Blacks, Williams wants to add Olympic gold. He won't have to look far for family support, with his sister, Niall, selected in the title-chasing New Zealand women's team.
The sevens format has surged in popularity since its inclusion on the Olympic program, and the rewards are being spread more widely than ever. Countries such as Kenya and the United States have won stops on the world series circuit, and are ranked 6th and 7th behind southern hemisphere powers Fiji, South Africa, New Zealand, Australia and Argentina. American Madison Hughes led the world series with 331 points in the 2015-16 season. American speedster Perry Baker was second behind South Africa's Seabelo Senatla for most tries scored and most line breaks.
Australia won the women's world series, reaching the final in four of the five tournaments to outpoint second place New Zealand, the dominant team in 2014-15. Canada and England were equal on points in third place.
The women's squads in Rio will feature players lured from sports such as basketball, volleyball and track and field. As it catches on, there'll be more professionals, and increased competition.
''New Zealand had been the benchmark ... ever since I had started playing rugby. Everything we trained for and played for can subconsciously be aimed around beating them,'' Australia's Alicia Quirk said. ''But this series turned out to be the most competitive season yet - the gap between teams has definitely closed.''
Spain was the last of 12 teams to qualify in each of the men's and women's tournaments. The Spanish men had a stunning upset win over world series regulars Samoa in the last-ditch repechage, a victory which playmaker Patricia Garcia said inspired her women's team to its victory over Russia in Dublin the following week.
Ruck, maul, scrum - all physical contests for the ball. Hooker, prop, wing - all playing positions.
Each competition will feature 12 teams divided into three pools, with the top eight advancing to the quarterfinals. U.S. teams got tough draws: the men were grouped with Fiji, Argentina and Brazil, and the women were grouped with Australia, Fiji and Colombia.