How to play

The bout starts at the shikiri. Press Space to charge: that is the tachi-ai, and the rules require both fists on the clay before it.

W / S drive forward, give ground
A / D step sideways
Shift drop your hips - lower centre of mass, more drive, less reach
J take a hold. An inside hand on the belt (shitate) beats an outside one (uwate); two inside hands is morozashi
K turn him over. With a belt hold that is a throw; with nothing but a hand on him it is a twist-down. Hold A or D to choose the side
L slap or pull him down. Only works on a man who has put his weight on you
I lift him off the clay - needs a deep grip and a real weight advantage
U take his leg
O pivot at the tawara - the last resort when your heels are on the bales
R let go , / . swing the camera

On a phone or tablet, touch buttons appear during a bout: the arrows on the left drive and step, the buttons on the right are the same actions as the keys above (Hips stays down until you tap it again). Hold an arrow while you tap Throw or Trip to choose the side.

How you lose

You are out when any part of you touches outside the ring, or when anything but the soles of your feet touches the clay inside it. Lean on your opponent and he is holding part of your weight: that costs you the traction you need to push, and if he takes the support away you are already falling. That is what a slap-down is.

What the ring is

A circle 4.55 m across, bounded by half-buried straw bales. Four of them - the tokudawara - sit slightly outside the line at the four cardinal points, so there is a little more floor there to fight back from. The two white shikiri-sen at the centre are 70 cm apart, on a clay platform 6.7 m square. A top-division bout is stopped for a water break after 4 minutes.

Kimarite 決まり手

The Japan Sumo Association recognises 82 winning techniques and 5 non-technique results - 87 named outcomes in all. Every bout in this game is named from that list. The ones you have been credited with are highlighted.

Six categories: -. .

What is real here, and what is not

This is an independent reimplementation of sumo, written from published sources. It is not affiliated with, endorsed by or connected to the Japan Sumo Association, any sumo stable, or any wrestler. All fifteen opponents and the player's own ring name are invented.

Sourced

The list of 82 kimarite and 5 non-technique results, their Japanese names, their kana readings and their six categories, transcribed from the Japan Sumo Association's own published list at sumo.or.jp and cross-checked name-for-name against the English and Japanese Wikipedia articles. The category counts - basic 7, throwing 13, leg-tripping 18, backward body drops 6, twist-downs 19, special 19 - were counted from the parsed table, not taken on trust.
The English one-line glosses, from the English Wikipedia article, which cites NHK. The JSA's own pages illustrate each technique but carry no prose definition.
The ring: 4.55 m across (15 shaku), straw bales, four tokudawara set slightly outside the circle at the cardinal points, shikiri-sen 90 cm long and 6 cm wide 70 cm apart, a clay platform 6.7 m square.
The winning conditions, shini-tai and kabai-te, the four-minute top-division limit and the water break, the tachi-ai fist-down rule, the eight kinjite, and that there are no weight classes.

Reconstructed - and this is the larger half

No published model exists, that I could find, of how two heavy bodies couple through a belt grip. So the dynamics here are mine. The forms are textbook rigid-body mechanics - an inverted pendulum over a foot base, a friction bound of μN, a force at chest height resolved into a force at the centre of mass plus a moment - but every number is a choice I made:

the coefficient of friction of a bare foot on sanded clay (0.62);
how much of your weight your opponent can be made to carry, and what that costs you;
grip strength, grip-breaking force, reach, stance width, how fast a hold can be switched;
the tachi-ai impulse, the cost of a lift, every opponent's mass and skill;
how far outside the circle the four tokudawara sit - the sources say that they do, but none of them says by how much.

A game that presented reconstructed physics as if it were sourced would be worth less than one that says which is which. The technique names are documented. The mechanics that produce them are not, and the classifier sitting between the two is the only part of the chain that can be checked against anything published.

Deliberate differences from the sport

A bout is decided by one referee and no judges: there is no mono-ii, no torinaoshi and no rematch. Shini-tai and kabai-te are applied automatically by a numeric rule that no source states.
The eight kinjite are not implementable here because the controls offer no way to commit one; nobody is ever disqualified.
The simulation reaches 18 of the 87 documented results - the ones its action set can create. The classifier knows all 87 and every one of them is proved reachable from a feature record, but the physics does not make backward body drops or the rarer leg trips. That 18 is a measured number: the page harness re-counts it over four thousand simulated bouts and fails if this sentence has drifted. The list dialog shows the whole table regardless.
No ceremony: no dohyo-iri, no salt, no chikara-mizu, no yobidashi, no gyoji.
Fifteen days against fifteen invented opponents; no banzuke, no ranks, no promotion beyond a kachi-koshi counter.

Full sources, the exact method, and the harness counts are in CREDITS.txt in this bundle.

Grand Sumo 大相撲

Basho over