Sumo is considered by many to be Japan’s national sport, with many ritual elements that originate in Shinto religion.
With all that has existed for over 2000 years, only professional sport has become the first part of the Edo period (1603-1868).
Fighters, called rikishi bear no other equipment than a silk-called mawashi belt that is wrapped repeatedly around waist, passed between the legs and tied with a knot at the back. There are no rules on how to be wrapped belt, some prefer to wrap rikishi close to everything and to wet with some water, and others, by contrast, prefer a more free law. In tournaments, but not in training under the belt is caught a kind of apron-strings called Sagar-made (soft fighters in lower categories, starched and strengthened by those of the two higher classes, and makuuchi juryō). The workouts are used belts made of cotton.
If a rikishi is somehow going to be completely loosening the belt during a match (and thus remain naked) - rare thing, but his example: Asanokiri happened in 2000 - fighter is disqualified automatically.