Originated in Japan, the only country where it is practiced professionally, sumo is a competitive full-contact sport where a wrestler (rikishi) attempts to force another wrestler out of a circular ring (dohyo) or to touch the ground with anything other than the soles of the feet. Sumo matches take place in a a ring (dohyo), 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. 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 dohyo.
