The winner of a Sumo bout is mainly determined by two rules:

- The first wrestler to touch the ground with any part of his body other than the soles of his feet loses.

- The first wrestler to touch the ground outside the circle loses.

On rare occasions the referee or judges may award the win to the wrestler who touched the ground first; this happens if both wrestlers touch the ground at more or less the same time and it is decided that the wrestler who touched the ground second had no chance of winning as, due to the superior sumo of his opponent, he was already in an irrecoverable position. The losing wrestler is referred to as being shini-tai (“dead body”) in this case.

There are also a number of other rarely used rules that can be used to determine the winner. For example a wrestler using an illegal technique (or kinjite) automatically loses, as does one whose mawashi becomes completely undone. A wrestler failing to turn up for his bout (including through a prior injury) also automatically loses (fusenpai). After the winner is declared, an off-stage gyoji (or referee) determines the kimarite (or winning technique) used in the bout, which is then announced to the audience.

Matches often last only a few seconds, as usually one wrestler is quickly ousted from the circle or thrown to the clay. However they can occasionally last for several minutes. Each match is preceded by an elaborate ceremonial ritual. The sportsmen themselves are renowned for their great girth, as body mass is a winning factor in sumo.