Rugby union is played between two teams – the one which scores more points wins the game. Points can be scored in several ways: a try, scored by grounding the ball in the in-goal area, is worth 5 points and a subsequent conversion kick scores 2 points; a successful penalty kick or a drop goal each score 3 points. The values of each of these scoring methods have been changed over the years.
Each team starts the match with 15 players on the field. During the match, players may be replaced (for injury) or substituted (for tactical reasons). A player who has been replaced may not rejoin play unless he was temporarily replaced to have bleeding controlled; a player who has been substituted may return temporarily, to replace a player who has a blood injury, or permanently, if he is replacing a front-row forward. In international matches, up to seven replacements are allowed; in domestic or cross-border tournaments, at the discretion of the responsible national union(s), the number may be increased to eight, of whom three must be sufficiently trained and experienced to provide cover for the three front row positions. Players in a team are divided into eight forwards (two more than in rugby league) and seven backs. Forwards are generally bigger and stronger, and take part in the scrum and lineout, while backs are generally smaller but faster, more agile and often the main points scorers for the team.
The field of play on a rugby pitch is as near as possible to a maximum of 100m long, and 70m wide. There are several lines crossing it, notably the half way line, the goal line/try line (on which the goal posts are located), the "twenty two", which is 22m from the goal line, and the dead ball line, which ideally is at least 10m but not more than 22m behind the goal line.
At the beginning of the game, the captains and the referee toss a coin to decide which team will kick off first. Play then starts with a drop kick, with the players chasing the ball into the opposition's territory, and the other side trying to retrieve the ball and advance it. If the player with the ball is tackled, frequently a ruck will result.
Forward passing (throwing the ball ahead to another player) is not allowed. The ball can be passed laterally or backwards, but cannot be thrown forward. The ball tends to be moved forward in three ways—by kicking, by a player running with it and passing it to a teammate who continues the run, or within a scrum or maul. Unlike in American football, "blocking" is not allowed, so only the player with the ball may be tackled or rucked. When a ball is knocked forward by a player with his/her arms, a "knock-on" is committed, and play is restarted with a scrum.
When the ball leaves the side of the field, a lineout is awarded against the team which last touched the ball. The lineout is usually awarded at the position where the ball left the field of play but if the ball is kicked directly into touch from outside the "twenty-two", or if a team plays the ball back into its own "twenty-two" and the ball is then kicked directly into touch, the lineout is awarded at a point opposite where the ball was kicked. To form a lineout, players from each team line up in parallel lines, at least 1m apart and at least 5m from the sideline; a player (usually, but not necessarily, the hooker) from the team that was awarded the lineout throws the ball down the gap between the two lines of players, who can jump or be lifted in an attempt to secure possession of the ball. Lineouts are one of the chief differences between the two rugby codes, as they do not occur in rugby league.
Games are divided into 40-minute halves, with a break in the middle. The sides exchange ends of the field after the half-time break. Stoppages for injury or to allow the referee to take disciplinary action, do not count as part of the playing time, so that the elapsed time is usually longer than 80 minutes. The referee is responsible for keeping time, even when—as in many professional tournaments—he is assisted by an official time-keeper. If time expires while the ball is in play, the game continues until the ball is 'dead', and only then will the referee blow the whistle to signal half-time or full-time; but if the referee awards a penalty or free-kick, the game continues.
Tries are scored between the goal line and the dead ball line. The goal line is treated as part of the in-goal area and a try can be scored if the ball is grounded with any part of it touching the goal line. The dead ball line is out of play, and a ball that touches or crosses the dead ball line, or that is held by a player who touches or crosses the dead ball line, is out of play.
Rugby goalposts are H-shaped, and consist of two poles, 5.6m apart, connected by a horizontal crossbar 3m above the ground. Unlike some other sports there are no goalkeepers, and the section underneath the crossbar has no special meaning. The original pitch dimensions were in imperial units, but have since been converted to the metric system.
There are three match officials: a referee, and two assistant referees. The latter, formerly known as touch judges, had the primary function of indicating when the ball had gone "into touch"; their role has been expanded and they are now expected to assist the referee in a number of areas, such as watching for foul play and checking off-side lines. In addition, for matches in high level competitions, there is often a television match official (TMO; popularly called the "video referee"), to assist with certain decisions, linked up to the referee by radio. The referees have a system of hand signals to indicate their decisions.
Common offences include tackling above the shoulders, collapsing a scrum, ruck or maul, not releasing the ball when on the ground, or being off-side. The non-offending team has a number of options when awarded a penalty: a "tap" kick, when the ball is kicked a very short distance from hand, allowing the kicker to regather the ball and run with it; a punt, when the ball is kicked a long distance from hand, for field position; a place-kick, when the kicker will attempt to score a goal; or a scrum. Players may be sent off (signalled by a red card) or temporarily suspended ("sin-binned") for ten minutes (yellow card) for foul play or repeated infringements, and may not be replaced.
