Sumo is a traditional Japanese sport in which two opponents attempt to force each other out of a ring. The sport is considered a national sport of Japan and has been practiced since the Edo period. It is a popular spectator sport, with tournaments held regularly throughout the year. SUMO wrestlers, or rikishi, are highly respected in Japan and are expected to adhere to strict rules of etiquette and behavior. The objective of the sport is to push or throw one's opponent out of the ring, or to touch the ground with any part of the body other than the soles of the feet.