There are two parallel white lines in the center of every sumo ring known as shikiri sen.
Ninety cm in length and 6 cm wide, they are painted directly onto the clay surface using enamel paint.
Rikishi must stay behind the line on their side before the initial clash.
In amateur sumo, no part of the hand may be in contact with the line. But in professional sumo, most wrestlers place their hands on the lines themselves.
A little-known fact is that there is no requirement to be close to the line at the faceoff. A rikishi can start the bout from any position he likes — even all the way back to the edge of the ring if he so wishes. That’s a tactic undersized Isegahama stable wrestler Shunba occasionally employed to throw larger opponents off.
The lines are touched up at the end of each day’s action by the yobidashi (ring announcers) with a couple of straw mats placed in a triangular shape above them to allow the paint to dry under the tarp, which is pulled over the ring.
Enamel paint is used because of the beating the lines take. Its toughness, however, means that the surface of the lines is slicker than the surrounding dirt.
That can sometimes lead to rikishi losing their footing after slipping on the lines. The narrowness of the shikiri sen ensures that such occurrences are rare.
The distance between the lines is just 70 cm. That might not seem like much, but it’s something that ensures wrestlers are about as far away from each other as football players are at the line of scrimmage.
Shikiri sen were introduced in the spring tournament of 1928. Although wrestlers had generally kept the same distance apart previously, sometimes they began a bout only a few centimeters away from their opponent.