The fast-paced rugby sevens format which was introduced into the Olympic Games program at the 2016 Rio Olympics will once again be used in Paris.

It is different from the traditional style of the sport, which contains 15 players on the field. In rugby sevens, only seven players are allowed on the field. 

Also in rugby sevens, a match lasts 14 minutes, divided into two halves of seven minutes each, with a break of one to two minutes between each half. In the traditional form of rugby, it consists of two halves of 40 minutes each with a 10-15 minute halftime. The way a scrum is played is also different between the two versions of the sport. In Olympic rugby, three forwards of each team face each other in a single line, while the other form of rugby usually has eight players from each side pushing against each other. 

Unlike traditional rugby, penalties in Olympic rugby are kicked as drop goals and not from a tee. 

Most Olympic rugby matches are 14 minutes long, split into two seven-minute halves. A two-minute break separates the first and second half. 

Each team consists of 12 players: seven on the pitch at any given time and five on the bench. Each team is permitted up to five substitutions throughout a match. Unlike in soccer, a player may re-enter a match in which he/she has been removed, though this spends an additional substitution. 

The object of rugby is to score more points than the opponent. The most direct way to do that is by scoring a “try.” A try occurs when one team carries the ball through the opponent's end of the pitch and across their goal line, touching the ball to the grass in the “try zone.” A try is worth five points, and offers the opportunity for a “conversion,” worth an additional two points. 

A conversion is scored by kicking the ball through the goal posts. The kick must be taken perpendicular to the spot in the try zone where the ball was touched down. For this reason, when possible, a try scorer will attempt to touch the ball down in the center of the try zone in order set up the easiest possible conversion attempt.  

If the opposition commits a major foul, the referee may award a penalty to the offended team. That team may choose to attempt a penalty drop kick toward their opponent’s goal posts if they are within range. If the kick goes through the goal posts, the kicking team is awarded three points. A player may also attempt a drop goal during open play, though the opposing team can interfere in this case. A successful attempt is also worth three points. 

Hence the name, there are seven positions in rugby sevens. Those positions are the following: 

• Loose-head prop: The left-most of three forwards in a scrum. On offense, expected to gain tough meters with power and strength, breaking tackles. On defense, expected to hold a firm front line in the center of play. 
• Hooker: The middle of three forwards in a scrum. Uses one leg to “hook” the ball backward to his scrum half. Similar offensive and defensive roles as the loose-head prop. 
• Tight-head prop: The right-most of three forwards in a scrum. Similar offensive and defensive roles as the other forwards. 
• Scrum half: The player who feeds the ball into the scrum, then retrieves it to start and attack. On offense, transitions play between the forwards and the backline. On defense, provides an organizing role and often covers gaps between the forwards. 
• Fly half: Often the first person to receive a pass from the scrum half after a scrum. On offense, acts as the playmaker, finding space and springing breakaways through creative passing. On defense, covers the middle of the pitch, forcing the opposing attack out wide. 
• Center: The second-widest-playing member of the backline, between the center and the wing. On offense, combines playmaking ability with speed and elusiveness, scoring often. On defense, helps the center cover the middle of the pitch and stop opposing breakaways. 
• Wing: The outermost player on the backline. On offense, the most dynamic try-scoring threat, capable of long breakaway runs at any moment using speed and elusiveness. On defense, expected to chase down opposing breakaways and make try-saving tackles. 

Courtesy: World Rugby

There are three types of set pieces in Olympic rugby; scrum, lineouts and kick-off. 

If play is stopped for a minor infringement (accidental forward pass, knock-on, offside, etc.), a scrum is awarded in the other team’s favor. During a scrum, each team’s forwards bind together and engage the other team’s forwards at the shoulders. The possessing team’s scrum half then feeds the ball beneath the scrum, where his team’s hooker tries to knock it back to a position where the scrum half can retrieve it, starting an attack. 

When the ball goes out of bounds over the touchline, play is restarted with a lineout awarded to the team that did not send the ball out of play. One player from that team takes the ball on the touchline, ready to throw it back in play to his/her teammates. Three players from each team gather in front of the thrower. Two of the players (usually both props) lift the third up in the air. The thrower attempts to complete a pass to his/her team’s lifted player. The opposing team’s lifted player attempts to disrupt or intercept that pass. Whichever team manages to secure possession begins an attack. 

A kick-off starts play at the beginning of each half and restarts play after a try/conversion attempt. The kicking team lines up just behind the halfway line, where the kicker drop kicks the ball toward the opponents. The kicker can elect to kick it as deep as possible, or attempt to kick it the minimum 10 meters so that his team might have a chance to recover the kick and maintain possession. Once the ball travels 10 meters, it is a live ball.