Sumo is a Japanese style of wrestling and Japan's national sport. It originated in ancient times as a performance to entertain the Shinto gods. Many rituals with religious background are still followed today.

The basic rules of sumo are simple: the wrestler who first touches the ground with anything besides the soles of his feet, or who leaves the ring before his opponent, loses. Fights take place on an elevated ring, called a "dohyo", which is made of clay and covered in a layer of sand. The fights themselves usually last only a few seconds, or in rare cases, about a minute.

At the top of the sumo wrestlers' hierarchy stand the yokozuna (grand champion). Once a wrestler reaches the rank of yokozuna, he cannot lose this status but he will be expected to retire when his results begin to worsen. Many former wrestlers remain active in the sumo world as members of the Japan Sumo Association.

Most elite wrestlers are highly trained athletes between 20 and 35 years old. They typically live together in residential and training complexes, called "stables", where all aspects of life, from sleeping and eating to training and free time, are strictly regimented by the coach, called the "stable master".

There are no weight restrictions or classes in sumo, meaning that wrestlers can easily find themselves matched off against someone many times their size. As a result, weight gain is an essential part of sumo training. The typical sumo dish, chanko nabe, is a hearty stew full of vegetables, meat and fish.

Six tournaments are held every year, each one lasting 15 days. Three of the tournaments are held in Tokyo (January, May, September), and one each in Osaka (March), Nagoya (July) and Fukuoka (November).