Sumo is a traditional Japanese sport that has been practiced since ancient times. It is a form of wrestling in which two opponents, known as rikishi, attempt to force each other out of a circular ring or into touching the ground with any part of their body other than the soles of their feet. The sport is highly ritualized and is considered a national sport in Japan. SUMO is also popular in other countries, including the United States, where it is often performed in exhibitions.