Sumo wrestlers are usually very large, appearing overweight to the point of obesity, although they also tend to be very strong and are fit enough to cope with intense physical activity over short periods of time. While competing, they wear a special loincloth called a mawashi and also do their hair in a particular form of topknot according to their rank. A match is over if a wrestler is thrown out of the ring by his opponent, or if any part of his body except the soles of his feet touches the ground.
Sumo competitions (basho) at the top level feature three ranks of wrestlers, which are yokozuna, Ozeki and maegashira (highest first). Becoming a yokozuna is the pinnacle of achievement in sumo, and the rank is not awarded lightly; there are typically only one or two competing at any one time, and there may not be any.
Sumo is a very traditional sport, and there are many written and unwritten rules concerning competitors' appearance and behavior. In recent years, significant numbers of non-Japanese wrestlers have started to compete in Japan, particularly from Mongolia and the former Soviet Union. This has led to controversy, as these outsiders tend not to have the same respect for sumo's traditions, instead treating it like any other sport where any practice within the letter of the regulations is fair game.