The most popular sport in the world, football can trace its roots back to ancient China – according to historians, the game played back then used the skulls of adversaries defeated in battles instead of a ball. Over the years, the practice of two rival groups playing for control of a ball in a field spread through the East, ancient Greece and the Roman Empire.

However, the origins of modern football lie in England. Historical reports state that, in the year of 1175, inhabitants of English towns kicked around a leather ball, representing the heads of their enemies, to symbolise the expulsion of Nordic invaders. The participants had to kick the ball along a route up to two kilometres in length along the town’s streets. The practice, however, was banned for the following four centuries.

At the start of the 19th century, the sport was adopted as a physical activity by three elite schools in England, and it gained popularity. As a result, it was necessary to standardise the rules, as touching the ball with both the hands and feet was permitted in some places. From this point onwards, football and rugby started to become distinct sports.

In 1863, the Football Association was founded to establish rules permitting championships to be played throughout the world. Eight years later, the first association football competition – the FA Cup, which exists to this day – was held.

Football was professionalised in 1885 and England, then a global power, helped the sport to spread across the world. In 1894, football was introduced to Brazil by Charles Miller in the city of Santos, and in due course it became the country’s most popular sport.

The year 1904 saw the establishment of the Fédération Internationale de Football Association (FIFA), the only entity authorised to organise international competitions, always based on the rules of Football Association. The first competition was planned for 1906, but in the end it was cancelled.

Football’s first appearance in the Olympic programme was at the 1900 Games in Paris, as an exhibition sport and with clubs representing each country. The sport entered the programme definitively in 1908, when the Games were held in London, with FIFA’s endorsement.

Since then, the only year in which there was no football competition at the Olympics was 1932, in Los Angeles, due to a disagreement between FIFA and the International Olympic Committee (IOC) about whether the players needed to be amateurs. Women first played football at the Olympic Games in 1996, in Atlanta.

The Olympic football competition is played by footballers up to the age of 23, except three players with no age limit on each team. Women’s teams have no age restrictions.

The competition has a first phase, in which the teams (16 for men and 12 for women) are divided into groups of four teams each. All countries play each other, and the two best in each group go through to the elimination round. In the women’s competition, the two best third-placed teams also go into the quarter-finals.

If a knock-out match ends with the scores level, there are two 15-minute periods of extra time. If the game is still drawn, a penalty shoot-out takes place. The semi-final winners play for the gold medal, while the losing teams compete for bronze.