The Rugby World Cup, started in 1987, is a quadrennial international rugby championship contested by the top 20 national men’s rugby teams in the world. The 2015 tournament, which lasts six weeks, began on Sept. 18th and is being hosted by England. The final will be held at Twickenham Stadium in London on Oct. 31.

Japan defeated South Africa 34-32 in the first great upset of the 2015 Rugby World Cup . The surprise group-stage victory was entirely unprecedented. South Africa had only lost to three other teams in the history of the World Cup: Australia, New Zealand, and England. It had also been 24 years since Japan last won a World Cup game. The match represents a pivotal moment for rugby in Japan, where the 2019 World Cup will be hosted.

The winners of the tournament are awarded the William Webb Ellis Cup. The trophy is named after an Anglican clergyman who invented the sport of rugby in 1823. According to legend, Webb Ellis simply picked up the ball during a soccer game and ran with it towards the goal, inspiring the new sport of rugby.

The Rugby World Cup is organized by the sport’s worldwide governing body, World Rugby, which  was formerly known as the International Rugby Board. The association, founded in 1886, has 100 full members and 17 associate members, and is headquartered in Dublin, Ireland.

Twelve of the 20 teams in the tournament qualify automatically by finishing third or better in the group stages of the previous Rugby World Cup. The remaining eight teams qualify by region, with Europe and the Americas both receiving two qualifying places and Africa, Asia, and Oceania one place each. Final qualifiers are decided through a play-off.

The tournament is divided into a group stage and a knockout stage. The nations are divided into four groups of five teams. In the group stage, each team plays every other team in its pool once. Teams are awarded four points for a win, two points for a draw and none for a defeat. Teams can also score a bonus point by scoring four or more tries in one match or by losing by seven or fewer points.

The top two teams from each pool enter the knockout stage, with the third-place team falling out of the tournament, but automatically qualifying for the next Rugby World Cup. The knockout stage has eight teams and three rounds: A quarter-final, semifinal, and then the final. The winner of each group faces the runner-up of another group in the quarter-final. The losers of the semifinal matches play a consolation match for a bronze medal. 

New Zealand—the current title holder—South Africa, and Australia each hold two titles. England captured a title in 2003. New Zealand is the only country to reach every semifinal held since the Rugby World Cup was created.

Attendance has fluctuated over the history of the tournament. The average sits at around 1-2 million spectators each year. The most successful Rugby World Cup was the 2007 edition, held in France and attracting 2.3 million viewers, 35 per cent more than the 2011 tournament in New Zealand.

The officially-licensed Rugby World Cup 2015 video game was released in September 2015 on PC, PS3, PS4, Xbox 360 and Xbox One. IGN rated the game 1.5 out of 10, calling it "unbearable."