The game
Duration: A game of rugby consists of two halves of 40 minutes with injury time added on at the end of each half. This is not as long as you might expect, because physiotherapists are often allowed onto the pitch while play continues. 

Players: Each side consists of 15 players, divided into eight forwards and seven backs. A total of seven substitutes are allowed for international matches. (There are also seven and 10-man versions of rugby union, played almost exclusively at tournaments)

Officials: There is one referee assisted by two touch judges, who mark where the ball goes out of play, adjudge kicks at goal and inform the referee of foul play.

The object of the game is to score more points than your opponents. There are a number of ways to achieve this.

Try: A try is worth five points. It is scored when a player places the ball on the ground with downward pressure in the in-goal area between the try line and dead ball line of the opposition's half. 

There are four ways of scoring points

the kick at goal must go in between the poles and over the bar
and over the bar and unlike football

The Field

Tackling: Only a player in possession of the ball can be tackled. A tackled player must release the ball after he hits the ground. Neither he nor the tackler can play the ball until they are on their feet. It is illegal to high tackle above the shoulders, or to "spike" a player by deliberately upending him onto his head. The same goes for the late tackle - taking the player after he has passed or kicked the ball.

Set play/set pieces

Scrum: 

Scrum during Lahore Vs Calcutta game

The eight forwards from each team bind together and push against each other. The scrum-half from the team that has been awarded possession feeds the ball into the centre of the scrum from the side most advantageous for his hooker.

The ball must be fed straight down the middle of the tunnel and the hookers must not contest for the ball until it is put in. If they do, a free-kick is awarded for "foot up".

Lineout: 

A maximum of seven and a minimum of three forwards line up parallel with each other between the five-yard and 15-yard lines. The hooker of the team in possession throws the ball in, while his opposite number stands in the "tramlines" - between the touchline and the five-yard line.

All players not involved in the lineout, except the scrum-half, must retire10 yards.

The ball must be thrown in straight down the middle of the lineout and the hooker must not cross into the field of play while throwing in.