When it comes to rules and regulations, the ruck is one of the more complex parts of rugby union.When a tackled player goes to ground, they must release the ball immediately.

As soon as that happens, the opposition will want to get their hands on the ball, and the team in possession will not want to give it away.

According to the laws, "the ruck is a phase of play where one or more players from each team, who are on their feet, in physical contact, close around the ball on the ground".

So to gain possession, both sides must try to drive over the ball to make it available for their team-mates.



HANDS IN THE RUCK
None of the tackler's team-mates can attempt to handle or pick up the ball once the ruck has formed.

Team-mates of the tackled player can use their hands, but only if they are on their feet.

Referees often blow up for penalties because a player off their feet or from the tackler's team has used a subtle hand to bring it back to their side.

But because of the sheer number of bodies involved in rucks, referees can sometimes miss this particular infringement.



JOINING A RUCK
All players must join the ruck from behind the 'hindmost' foot of the last player.

They must bind with one arm round a team-mate at the very back of the ruck.

Players cannot take shortcuts and join from the sides.

If the referee spots this, a penalty will be given to the non-offending team.



USING THE BOOT
The ball can often get stuck under a pile of bodies, making it difficult for either team to make it available.



Dangerous rucking is an instant penalty
Players are allowed to free the ball by using their boot. This term is called 'rucking'.

However, they must ensure they do not make contact with players' heads or tread on bodies intentionally.

Referees are particularly strict on this law for safety reasons, so reckless rucking can mean time in the sin-bin or even a red card.



DIVING IN
All players joining a ruck must be on their feet.

But sometimes players dive in off their feet in an attempt to slow the ball down, allowing defences to re-group.

Referees are particularly strict on this.



BALL NOT FREE
If the ball does not come out of a ruck after about five seconds, the referee will award a scrum to the team he considers to have the greater forward momentum in the ruck.

The line-out is another awesome sight in rugby union.

It is a way of restarting play after the ball has been knocked or kicked out of play past the touch line.

The line-out consists of three to eight players from each side, up to 16 in total, and is taken where the ball went out of play.

The aim of each player is simply to get their hands on the ball for their team.

So how does it work? The advantage is with the team throwing in.

They get the ball because they were not the team who last touched the ball before it went out. They also get to decide how many players will make up the line-out.



FORMING A LINE-OUT




The eight forwards and the scrum-half are the players who make up the line-out.

The most important players are the hooker, the two second rows and scrum-half. They are responsible for getting the ball out to the backs or for the rest of the forwards.

That does not mean the other players have nothing to do. Far from it.

The line-out must be formed past the five-metre line and no more than 15m in from the touchline, and both teams must have a one metre gap between them.

If the referee decides one team has purposely closed the gap, a penalty will be awarded to the other team.



LINE-OUT THROWS




The hooker is usually the player with the job throwing the ball into a line-out. Their aim is to find the "jumpers", usually the two second rowers.

But this is not easy. The other team also want the ball, so they'll be doing all they can to upset the hooker's throw.

The hooker gets a call from one of the jumpers or the scrum half, usually in a code no-one except your team understands, on who to aim the throw at.

They must stand behind the touch line when they make their throw.

And the throw must be deadly straight, otherwise the referee will have the line-out taken again, but this time the opposition get the throw in.



RETAKEN THROWS




The line-out may look very simple, but it has plenty of laws every player must follow:

The ball must be thrown straight

All players not in the line-out must be 10m behind the last man in the line

No player can use a one of the opposition to use as support when they are jumping

No player is allowed to push, charge or hold another player in the line-out

No player can be lifted before the ball is thrown

No jumper can use the outside of their arm to catch or deflect the ballDepending on how serious the offence is, the referee will either award a penalty or free-kick to the team who did not make the offence.

Rugby union is played by two teams of 15 players.Although the aim of the game is simple, there are many laws which make can make it hard for the new viewer to keep track of what is going on.

Here BBC Sport runs through the very basics of the game and, to the right, you can click on the links to find our more on the various rules of rugby union.



AIM OF THE GAME


Jonny Wilkinson scores the winning points in the 2003 World Cup final


The aim of the game is very simple - use the ball to score more points than the other team.

You can run with the ball, kick it and pass it, but passing forwards is not allowed.

Rugby union is a contact sport, so you can tackle an opponent in order to get the ball, as long as you stay within the rules.

There is a referee, aided by two touch judges (one on each side of the pitch), to decide how the rules should be applied during a game.

There are several ways to score points.

• A try - five points are awarded for touching the ball down in your opponent's goal area.
  
  
• A conversion - two points are added for a successful kick through the goalposts after a try
  
  
• A goal kick - three points are awarded for a penalty kick or drop goal through the posts

If both teams score the same amount of points, or no points are scored, then the match is a draw. In some cases, extra time is played to decide who wins.



DURATION
A game of rugby union has two periods of 40 minutes each. In international matches the referee will stop the clock for stoppages.

Between the two halves, there is a maximum 10-minute interval, after which both teams change ends.

The referee's whistle indicates the start and finish of the half.

Extra time will only be played if it's a knockout competition.



KICK-OFF
Before the start of the match, the referee tosses a coin to decide which team will kick off the match.

The captain of the team that wins the toss gets to decide which end he wants to attack first, or whether his side or the opposition will kick off.

The game is started by a place kick or a drop kick from the middle of the halfway line.

The ball must travel forwards at least 10 metres from the kick-off. If it does not, the opposition get the choice of a scrum or line-out on the halfway line, with the advantage of the feed or throw.

If a penalty or drop goal is scored during the game, play is restarted with a drop kick from the halfway line. The team that has conceded the points takes the kick.



THE BALL
Rugby union is played with an oval-shaped ball.

All balls must be between 28cm and 30cm in length (approximately 11-13 inches).

Most full-size balls weigh between 383 and 440 grammes (approximately 13.5-15.5 ounces)

The attacking line is where the attackers line up. 
The defensive line is where the defenders line up. 
The gain-line is always extended along the middle of a scrum or lineout. 
The offside line can vary (e.g. the back foot of a scrum or 10m back from the lineout). 
The tackle line is basically where the attackers and defenders meet. It will vary depending on the 
defensive system and defensive capabilities of the team. It is usually nearer the attacking line than 
the defensive line.