Sumo is a competitive contact sport where a wrestler (rikishi) attempts to push another wrestler out of a circular ring (dohyo) or force him touch the ground with anything other than the soles of his feet. The sport started in Japan, the only country where it is being practiced professionally.
The Sumo tradition is very old, and still includes many ritual elements, such as the use of salt for purification. The life of a rikishi is highly disciplined, with rules established by the Association of Sumo.
The Sumo matches take place in a ring with a diameter of 4.55 meters and 16.26 square meters, over a platform of clay mixed with sand. In the center there are two white lines, the Shikiri-sen, behind which the wrestlers position themselves at the start of the race.