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Two wrestlers meet in a ring, the dohyōdohyō 土俵The ring: a raised platform of packed clay. More on dohyō, about 4.55 metres across. You win by forcing the other man out, or by making him touch the ground with anything other than the soles of his feet. There are no weight classes, so a small wrestler can face one twice his size.

Striking with a closed fist, pulling hair and kicking the stomach or chest are all banned, and breaking a rule is an instant loss.

Every bout that's fought is recorded with how it was won, its kimaritekimarite 決まり手The winning technique. The JSA's official list has 82. More on kimarite, and the Japan Sumo Association recognises 82 of them. When a man's opponent doesn't turn up, he wins by default, a fusenshōfusenshō 不戦勝A win by default, when the opponent doesn't turn up. More on fusenshō, with no technique to record.

Before each basho the Japan Sumo Association publishes the banzukebanzuke 番付The official ranking list, published before each tournament. More on banzuke, the official ranking sheet. It holds for all 15 days, and the results decide the next one.

There are six divisions. Only the top two, makuuchimakuuchi 幕内The top division: 42 wrestlers, from yokozuna down to the maegashira. More on makuuchi and jūryōjūryō 十両The second division, and the lowest that's paid a salary. More on jūryō, are paid a monthly salary. In makuuchi the ranks run down from yokozunayokozuna 横綱Grand champion, the top rank. A yokozuna can't be demoted. More on yokozuna, the grand champion, through ōzekiōzeki 大関Champion, the second-highest rank. More on ōzeki, sekiwakesekiwake 関脇The third rank, just below ōzeki. More on sekiwake and komusubikomusubi 小結The fourth rank, the lowest of the named ranks above maegashira. More on komusubi to the numbered maegashiramaegashira 前頭The numbered rank-and-file of the top division. More on maegashira, up to 42 men in all. Every rank has an East and a West side, and East is a fraction higher.

More wins than losses, kachi-koshikachi-koshi 勝ち越しA winning record for the tournament: at least eight wins from 15, or four from seven. More on kachi-koshi, usually takes a man up the next banzuke, and a losing record usually takes him down. The top two ranks are the exception: an ōzeki drops only after two losing basho in a row, and a yokozuna is never demoted.

In Japan the top division fights from about 4 pm until just before 6 pm, so on the east coast it's on around dinner time.