Sumo is a competitive full-contact sport where a wrestler (rikishi) attempts to force another wrestler out of a circular ring (dohyou) or to touch the ground with anything other than the soles of the feet. The sport originated in Japan, the only country where it is practiced professionally. It is generally considered to be a gendai budou (a modern Japanese martial art), though this definition is incorrect as the sport has a history spanning many centuries. Many ancient traditions have been preserved in sumo, and even today the sport includes many ritual elements, such as the use of salt purification, from the days when sumo was used in the Shinto religion. Life as a rikishi is highly regimented, with rules laid down by the Sumo Association. Most sumo wrestlers are required to live in communal "sumo stables" known in Japanese as heya where all aspects of their daily lives—from meals to their manner of dress—are dictated by strict tradition.
Over the rest of Japanese recorded history, sumo's popularity has changed according to the whims of its rulers and the need for its use as a training tool in periods of civil strife. The form of wrestling combat probably changed gradually into one where the main aim in victory was to throw one's opponent. The concept of pushing one's opponent out of a defined area came some time later.
Also, it is believed that a ring, defined as something other than simply the area given to the wrestlers by spectators, came into being in the 16th century as a result of a tournament organized by the then principal warlord in Japan, Oda Nobunaga. At this point wrestlers would wear loose loincloths, rather than the much stiffer mawashi of today. During the Edo period, wrestlers would wear a fringed kesho-mawashi during the bout, whereas today these are worn only during pre-tournament rituals. Most of the rest of the current forms within the sport developed in the early Edo period.
Professional sumo (大相撲) can trace its roots back to the Edo period in Japan as a form of sporting entertainment. The original wrestlers were probably samurai, often rounin, who needed to find an alternative form of income. Current professional sumo tournaments began in the Tomioka Hachiman Shrine in 1684, and then were held in the Ekou-in in the Edo period. They have been held in the Ryougoku Kokugikan since 1909, though the Kuramae Kokugikan had been used for the tournaments in the post-war years until 1984.
Shinto has historically been used as a means for Japanese nationalism and ethnic identity, especially prior to the end of World War II. It has served to symbolize and provide a sense of belonging, to identify and unify the Japanese people culturally, and to serve as a barrier demarcating the Japanese from other peoples, providing them with a sense of cultural uniqueness. In its association with Shinto, sumo has also been seen as a bulwark of Japanese tradition.
Shinto ritual pervades every aspect of sumo. Before a tournament, two of the gyouji functioning as Shinto priests enact a ritual to consecrate the newly-constructed dohyou, and various Shinto rituals are associated even with the practice dohyou at heya. Both the dohyou-iri, or ring-entering ceremonies performed by the top two divisions before the start of their wrestling day, and in the rituals performed by both combatants immediately before a bout, are derived from Shinto. It retains other Shinto associations as well. The yokozuna's ring-entering ceremony is regarded as a purification ritual in its own right, and is occasionally performed at Shinto shrines for this purpose.