Sumo ( or sumo wrestling ) is a sport from Japan where heavy men try to push one another out of a ring or onto the ground .
Many ancient traditions have been preserved in sumo , and even today the sport includes many ritual elements , such as the use of salt purification , from the days when sumo was used in the Shinto religion . Life as a rikishi is highly regimented , with rules laid down by the Sumo Association .