Sumo Wrestling

Sumo matches take place in a dohyō (土俵): a ring, 4.55 metres (14.9 ft) in diameter and 16.26 square metres (175.0 sq ft) in area, of rice-straw bales on top of a platform made of clay mixed with sand. A new dohyō is built for each tournament by the yobidashi. At the center are two white lines, the shikiri-sen, behind which the wrestlers position themselves at the start of the bout. A roof resembling that of a Shinto shrine may be suspended over the dohyō.
Professional sumo
Professional sumo is organized by the Japan Sumo Association. The members of the association, called oyakata, are all former wrestlers, and are the only people entitled to train new wrestlers. All practicing wrestlers are members of a training stable (heya) run by one of the oyakata, who is the stablemaster for the wrestlers under him. Currently there are 54 training stables for about 700 wrestlers.