Judo matches are fought between two people on a square mat measuring between 8 to 10 meters per side. There is one head referee and two assistant referees. Any one of 67 throwing techniques and 29 grappling techniques may be used to win.
Scores are awarded for various techniques, the highest being ippon, when you throw your opponent so that their back completely touches the mat. This ends the bout immediately, like a knockout in boxing. Another way to end the match is to compel the opponent to submit by saying "Maitta!" (I give up) or tapping their hand twice on the mat or on their body. You can also gain points for skillful attacks, even if they do not lead to ippon. The referees award points depending on how good these moves are, from wazaari to yuko and koka, in descending order. Two wazaari count as an ippon, ending the contest. Yuko and koka never add up to ippon, but the accumulation of lesser scores is frequently what determines who wins.
Holding your opponent down against the mat also results in an ippon after 25 seconds or when they submit. It counts as a wazaari after 20 seconds, yuko after 15 seconds, and koka after 10 seconds.
Points are awarded not only for good moves but also penalties committed by your opponent, such as stalling, moving out of the mat, or refusing to attack. Illegal or dangerous techniques, moreover, can lead to disqualification. There are several levels of rule infringement. The least serious is shido, but when committed twice it is counted as a more serious chui. Still more serious is keikoku. If the score at the end of the match is even, the three referees decide the winner by each raising a flag to signal who they think fought better.
One of the appeals of judo is the emphasis on etiquette, which shows that you respect your opponent. Contestants bow seven times before and after a match, for instance, bending their upper bodies forward at an angle of about 30 degrees. They bow when they enter and leave the competition area, before stepping onto and after coming off the mat, when facing the opponent at the start and end of a match, and when the referee announces the result.
Photos: (from top) A diagram of a judo mat. (from Illustrated Martial Arts and Sports in Japan, published by Japan Travel Bureau; illustrator, Masaki Matsushita); The Jigoro Kano Cup International Judo Tournament (Kodokan Judo Institute)