Each day is structured so that the highest-ranked contestants compete at the end of the day. Thus, wrestling starts in the morning with the jonokuchi wrestlers and ends at around six o'clock in the evening with bouts involving the yokozuna. The wrestler who wins the most matches over the fifteen days wins the tournament championship (yūshō) for his division. If two wrestlers are tied for the top, they wrestle each other and the winner takes the title. Three-way ties for a championship are rare, at least in the top division. In these cases the three wrestle each other in pairs with the first to win two in a row take the tournament. More complex systems for championship playoffs involving four or more wrestlers also exist, but these are usually only seen in determining the winner of one of the lower divisions.
The matchups for each day of the tournament are announced a day in advance. They are determined by the sumo elders who are members of the judging division of the Sumo Association. As there are many more wrestlers in each division than matchups during the tournament, each wrestler only competes against a selection of opponents from the same division, though there can be small overlap between two divisions. With the exception of the san'yaku ranked wrestlers the first bouts tend to be between wrestlers who are within a couple of ranks of each other. Afterwards the selection of opponents takes into account a wrestler's prior performance.
For example, in the lower divisions wrestlers with the same record in a tournament are generally matched up with each other, and the last matchups often involve undefeated wrestlers competing against each other, even if they are from opposite ends of the division. In the top division, in the last few days, wrestlers with exceptional records often have matches against much more highly ranked opponents, including san'yaku wrestlers, especially if they are still in the running for the top division championship. Similarly more highly ranked wrestlers with very poor records may find themselves fighting wrestlers much further down the division.
For the yokozuna and ōzeki the first week and a half of the tournament tends to be taken up with bouts against the top maegashira, komusubi and sekiwake, with the bouts within these ranks being concentrated into the last five days or so of the tournament (depending on the number of top ranked wrestlers competing). It is traditional that on the final day the last three bouts of the tournament are between the top six ranked wrestlers, with the top two competing in the very final matchup, unless injuries during the tournament prevent this.
There are certain match-ups that are prohibited in regular tournament play. Wrestlers who are from the same training stable cannot compete against each other, nor can wrestlers who are brothers, even if they join different stables. The one exception to this rule is that training stable partners and brothers can face each other in a championship-deciding playoff match.
The last day of the tournament is called senshūraku, which literally means the pleasure of a thousand autumns. This colorful name for the culmination of the tournament echoes the words of the playwright Zeami to represent the excitement of the decisive bouts and the celebration of the victor. The Emperor's Cup is presented to the wrestler who wins the top division makuuchi championship. Numerous other (mostly sponsored) prizes are also awarded to him. These prizes are often rather elaborate, ornate gifts, such as giant cups, decorative plates, and statuettes. Others are quite commercial, such as one trophy shaped like a giant Coca-Cola bottle.
Promotion and relegation for the next tournament are determined by a wrestler's score over the 15 days. In the top division, the term kachikoshi means a score of 8–7 or better, as opposed to makekoshi, which indicates a score of 7–8 or worse. A wrestler who achieves kachikoshi almost always is promoted further up the ladder, the level of promotion being higher for better scores. See the makuuchi article for more details on promotion and relegation.
A top division wrestler who is not an ōzeki or yokozuna and who finishes the tournament with kachikoshi is also eligible to be considered for one of the three prizes awarded for "technique", "fighting spirit" and for defeating the most yokozuna and ōzeki the "outstanding performance" prize. For more information see sanshō. For the list of upper divisions champions since 1909 refer to the list of top division champions and the list of second division champions.
(source)