The playing surface is usually grass. Artificial surfaces are very rarely used at professional level.

Regular season games end at 90 minutes, even if the scoreline is level.

In domestic cup competitions and the knockout stages of international club and national team competitions, an additional 30 minutes - known as extra-time - is played, split into two halves of 15 minutes.

If the scores are still level after extra-time, a penalty shootout takes place. Here, five players from each team take turns to score. If the scores are still level after that, the team's remaining players step up for sudden death until there is a winner.

The sport has 17 rules known as the Laws of the Game, which were laid down and are governed by the International Football Association Board (IFAB). The laws are designed to be universal, but slight modifications are made to take into account factors such as age, gender and disabilities.

What is a foul in soccer?

In the team of 11 players, 10 are known as 'outfield' players, and are forbidden by the Laws of the Game from touching the ball with their hands or arms. Only the team's goalkeeper is allowed to use their hands, and only inside their penalty area. If the goalkeeper leaves the penalty area, they are subject to the same rules as the outfield players.

Handling the ball deliberately, tripping an opponent, and pushing an opponent are punished either by a direct free-kick - meaning the attacking team can attempt to score immediately when the referee signals for play to continue - that is taken from the position where the foul occurred or a penalty if the infringement occurs inside the penalty box of the fouling player's team.

Other fouls are punished by an indirect free-kick, which means at least one other member of the attacking team must touch the ball before a goal can be scored.

Watch: Five things you might not know about set-pieces

If the ball crosses the touchline, a throw-in is awarded to the team which did not touch the ball last. This is the only time outfield players are permitted to touch the ball with their hands. They must return the ball into play while holding it with both hands and with both feet on the ground. Failure to do so results in a foul throw, meaning the other team are given the throw.

A referee is appointed before each game and enforces the Laws of the Game. They have two assistant referees - one placed on the touchlines on opposite sides of the pitch and in opposite halves. A fourth official is present for professional games.

The referee can punish foul play by awarding a free-kick against the team of the offending player. If the foul occurs in the penalty area, a penalty kick is given to the attacking team. If the attacking team commits a foul in the penalty area, a free-kick is given to the defending team.

The referee signals to players using a whistle, and is the only official inside the playing area.

A team can have up to four players sent off and still finish the match. However, referees are instructed to stop matches prematurely if a team is reduced to fewer than seven players.

What is VAR?

In recent seasons, referees have been helped further by Video Assistant Referees (VAR). Previously, television replays were not used to help referees make a decision. Now, the referee has one or two colleagues, usually away from the stadium, who review four specific situations: cases of mistaken identity for yellow/red cards, potential infringements in the build-up to a goal (fouls or offside), direct red card decisions, and penalty decisions.

Goalline technology is also used to tell referees if the ball has crossed the goal line. The whole of the ball must be over the goal line for a goal to be awarded.

Football is governed at a global level by FIFA, the International Federation of Football Associations, based in Switzerland. It has six regional confederations attached to it: the Union of European Football Associations (UEFA), the Confederation of African Football (CAF), the Asian Football Confederation (AFC), the Confederation of North, Central American and Caribbean Association Football (CONCACAF), the Oceania Football Confederation (OFC), and the South American Football Confederation (CONMEBOL).

Each country has their own national football association, such as the English Football Association in England, known as the FA, or US Soccer in the USA.

Each national association organises competitions between clubs associated with them. The most renowned are the 'top five' European leagues: the German Bundesliga, the English Premier League, La Liga in Spain, Italy's Serie A, and Ligue 1 in France.

Each regional confederation organises competitions between clubs and also national teams. The most well known and lucrative club competition in the world is the UEFA Champions League. It is held annually and features the European teams that have finished highest in their respective national leagues. UEFA also organise the UEFA EURO, a European championship held every four years, which features national teams that have won through in the qualifying process.