Although women have joined the game in earnest, twice as many men will take part in Sydney, with 16 men's teams and eight women's teams competing.
The men play in a round-robin of four pools of four, the best two progressing to quarter-finals. The women play in two pools of four, the best two from each pool advancing straight to semi-finals. Each team in a pool earns three points for a win and one for a draw.
Olympic football is played under the same rules, barring age restrictions, as the international game. The field is 100 to 110 metres long and 64 to 75 metres wide. A centre line at halfway cuts across a centre circle 9.1 metres in radius. Each goal end has a penalty area, which is marked by two lines running at right angles to the goal-line and starting 16.5 metres outside each goalpost, and a line running 16.5 metres into the field parallel with the goal-line. The goal area is smaller, marked by lines that start at right angles to the goal-line 5.5 metres outside the goalposts and closed by a line parallel to the goal-line 5.5 metres inside the field. The goals stand 8 ft high and 24 ft wide. The football weighs between 14oz (410g) and 16oz (450g).
Football owes a deal of its popularity to its simplicity. Two teams of 11 players aim to score goals by kicking or heading the ball into the opposition's goal. The match lasts 90 minutes, with a 15-minute break at half time. A coin is tossed to determine which team kicks off and the winner chooses which end he wishes his team to play at in the first half. The teams swap ends at halftime.
At kick-off all players must be in their own half and the defending team must be at least ten yards away from the centre mark when the ball is kicked off and play commences. Kick-offs are used to restart play after goals and halftime. A goal is scored when the ball crosses the goal-line into the net. If the ball sits on the goal-line but does not pass it, no score is registered. When the ball is kicked out of a play, a throw-in, corner kick or goal kick is awarded against the team that put the ball out of play. The throw-in is given when the ball is put out of play across the sidelines of the field, a corner awarded to an attacking team if the ball is put out of play across the back line by the defending team, and a goal kick is given if the ball is put out of play across the back line by the attacking team.
Attacking players are deemed offside when they are closer to the goal-line than both the ball and two opposition players, which usually includes the goalkeeper. Any move they make with the ball from this position is invalid and a goal will not count. However, the player is not offside if he receives the ball directly from a goal kick. A free kick is awarded to the defending team where an attacking player is offside.
Interfering with other players in a way that does not constitute a legal tackle is a foul and results in a penalty. Players should be guided by a simple thought; play the ball, not the person. A free kick is awarded in most cases of a foul being committed and opposing players must stand at least ten yards back from the point at which the kick is being taken. There are two forms of free kick, an indirect free kick, for lesser offences, in which the ball must be passed to a team-mate before a shot can be taken at goal, and a direct free kick, for more serious fouls, including an intentional handball, where a player can take a direct shot at goal if he or she chooses.
A foul within the penalty area results in a penalty, a direct shot at goal, one man and ball against goalkeeper. The shot is taken at the penalty spot 11 metres out from the centre of the goalmouth.
The referee may caution players who commit serious offences. A yellow card results from persistent fouling, dissent or unsportsmanlike behaviour. A red card sees the player sent off. Serious offences include violence, any foul that is used to prevent a goal, and even spitting. Two yellow cards in one match constitute a red card.
Games that end in a draw in preliminary rounds, remain as draws. In quarter-finals onwards, a sudden-death rule applies in which the first goal scored in extra time wins the game. If the teams are still tied after two 15-minute extra periods, a penalty shoot-out is held. Each team gets five penalty kicks to decide the winner, but if even that cannot split the teams then penalties continue until one team misses and is vanquished.
