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This article describes the rules of judo. The main sections of the article describe the rules that apply to any situation in which judo is practiced, and those rules which apply only in judo competitions. Separate sections describe the history of the rules of judo, provide links to other sources of information on judo rules, and list the references for this article.
In practice and competition 
- Intentionally injuring an opponent is not permitted.
- Punching, kicking, and other strikes are not allowed.
- Touching the opponent's face is not allowed.
- Attacking joints other than the elbow is not allowed.
- Head dives are not permitted.
- The technique known as kawazu gake is not permitted.
- The technique known as kani basami is not permitted.
- Wearing any hard or metallic object during competition is not permitted. The penalty for violating this rule is hansoku make (see Penalties, below). This includes wedding rings, earrings, hard-plastic protective gear, hair-ties with metal parts, wristwatches, and even press-studs on underpants.
- Contestants must bow before stepping onto the mat.
- Contestants must bow to each other before and after practice or competition.
- Inappropriate behaviour, such as foul language and bodily gestures, is not tolerated.
In competition only 
- Stalling is not permitted.
- Using a defensive posture is not permitted.
- It is required to bow to the competition area.
- False attacks are not permitted. They are considered attempts to circumvent the prohibition against noncombativity.
- Disregarding the orders of the judge is prohibited.
- Awarding of ippon (一本) 'One full point'. Award of ippon decides the winner and ends the match.
- Awarding of waza-ari (技あり). 'One half point'. When two waza-ari are awarded in the same match, it is considered to be same as ippon and the match ends (the judge exclaims 'Waza-ari, awasete ippon')
- Awarding of yuko (有効). One score of waza-ari is considered greater than any number of yuko scores. Yuko is currently the smallest score that can be awarded.
- Awarding of koka (効果). Was introduced in 1975 and removed from IJF competition at the end of 2008. Any number of koka scores does not add up to a yuko score.
Two types of penalties may be awarded. A shido (指導) is awarded for minor rule infringements. A shido can also be awarded for a prolonged period of non-aggression. Each time a contestant is awarded a shido, the other contestant gets points according to how many shidos the opponent has, as if he had scored them himself. For the first shido a warning is given to the offending party (this replaces the previous practice of awarding a Koka), after that the opponent will yuko, waza-ari and ippon respectively for each shido attained (if the opponent has a waza-ari, and receives another from the opponent's shidos, he wins the match). After four shidos are given, the victory is given to the opponent, this is an indirect hansoku-make, and does not result in expulsion from the tournament. The penalty of hansoku make (反則負け) is awarded for major rule infringements, or for accumulating four shidos. If hansoku make is awarded for a major rule infringement, it results not just in loss of the match, but in expulsion from the tournament.
Competition area 
The competition area must be padded with tatami. The minimum allowable size is 14 x 14 meters. The match takes place in an 8 x 8 meter to 10 x 10 meter zone within this larger area. The surrounding space acts as a safety zone. When two competition areas are side by side, there must be at least a 3 meter safety zone between them.
Rules related to grips are primarily motivated by the desire to avoid stalling, to avoid providing undue advantage, or to reduce the chance of injury.
- Deliberately avoiding gripping is not permitted.
- In a standing position, it is not permitted to take any grip other than a "normal" grip for more than three to five seconds without attacking. A "normal" grip is one where the right hand grips some part of the left hand side of the opponent's jacket (and the left hand grips some part of the right hand side of the opponent's jacket.) A non-normal grip may involve grabbing the belt, or the trousers, or the wrong side of the jacket. (A non-"standard" grip is one that does not involve the traditional sleeve/collar grip. There are no time-limits related to non-"standard" grips as long as they are not non-"normal".)
- A "pistol grip" on the opponent's sleeve is not permitted.
- It is not permitted to insert the fingers inside the opponent's sleeve opening or trousers opening at any time. You are permitted to insert your fingers inside your own gi openings.
- Biting the opponent's gi is prohibited, as it grants another gripping point.
- Since 2010, it is not permitted to grab the legs or trousers, initially. As of the 9th of february 2013 it will no longer be permissable to touch the legs of the opponant whatsoever. It will also no longer be allowed to prevent your opponant from taking a grip and when he has a grip it is also no longer permissable to break that grip with two hands. The rationale behind these rules to remove the martial art element of judo and make it as entertaining a sport as possible for the spectator. These rules are to the dismay of the judo community.
Judo competitions typically have some safety-related rules related to age: chokes are prohibited under a certain age (typically 13), and arm bars are prohibited under a certain age (typically 16).
The duration of matches is also dependent on the age of the competitors. Match length is typically three minutes for children, five minutes for teenagers and young adults, and three minutes for 'masters' (adults thirty years of age or older).
Rules related to the gi are primarily related either to safety or to preventing contestants from wearing gis that prevent their opponent from being able to get a grip on them.
- The sleeves of the jacket are not allowed to be too short: they must extend down to no more than 5 cm above the wrists with the arms extended in front of the body.
- The legs of the trousers are not allowed to be too short: they must extend down to no more than 5 cm above the ankle.
- Excessive advertising on the gi must be avoided, and may result in a forced loss if an appropriate gi can't be found.
Medical treatment, illness, and injury 
The official IJF rules related to the provision of medical treatment and to the proper handling of situations involving illness or injury are relatively long and involved, since the exact nature and cause of an injury may themselves affect the awarding of the match, and since receiving some types of medical treatment, but not others, automatically ends the match. The latter fact makes it necessary for medical attendants at judo matches to have some understanding of this rather complex aspect of the rules of judo. The medical team is not allowed to enter the fighting area without permission from the mat judge, and if a contestant receives medical treatment he automatically forfeits the match. Nosebleeds, for example can not be treated by the medical team, the contestant must fix it himself with materials provided by the medical team, proper procedure is stuffing cotton balls up the nostrils, while applying tape around the head. If a contestant is rendered unconscious without a choking technique, and is unable to wake up, the medical team has to take immediate action and they can't wait for the contestant's consent, he forfeits the match automatically. A contestant can of course ignore any injuries he has, and keep fighting. This requries that it's not of any discomfort to the opponent, f.ex. bleeding over your opponent can cause penalties. If the bleeding is tried to be stopped three times, with no effect, the match is forfeited.
- Effect of Russian gripping strategies on the grip-related rules.
- The technique known as kani basami was banned in 1980 after Yasuhiro Yamashita suffered a broken leg while being thrown with it.
- Motivation for banning of head-dives.
- IJF Rules, Section 27.b.25
- IJF Rules, Section 27.b.32
- IJF Rules, Section 27.b.24
- IJF Rules, Section 27.b.34)
- See Angus (2006) pp. 15-18 for a detailed explanation of judo penalties.
- IJF Referee Rules, Section 1, Competition Area
- IJF rules, Section 27.a.1
- IJF rules, Section 27.a.10
- IJF rules, Section 27.a.12
-  Principles of Judo Choking Techniques
- IJF Rules, Section 3.d
- IJF Rules, Section 3.e
- see Angus, p. 29
- The IJF rules are the official published reference for the rules of judo competition (see External Links, below). However, rules can be changed by committee decision between official releases of the published rules, and these are not published on the IJF site.
- Mastering judo by Masao Takahashi et al., explains a number of aspects of the rules. General rules of competition, etiquette, and the penalty system are covered in Chapter 2. ISBN 0-7360-5099-X.
- The first chapter of Competitive judo: winning training and techniques, by Ron Angus, is devoted to explaining a number of aspects of the rules. ISBN 0-7360-5744-7.