From a competitors point of view, the contest rules are fairly simple. Which is how we will be examining the rules here. For a complete list of the Judo contest rules please see:
The IJF Detailed Explanation of the IJF Judo Refereeing Rules
The IJF Sports and Organization Rules
You can also view the 2024 Dee High Memorial Alaska State Judo Championships Referee Training Slides
The contest rules of Judo are setup as a safe way to simulate a fight and allow the students to practice their techniques against a resisting opponent. With this in mind, consider yourself the "good guy", in real life, bad guys rarely attack alone. One of the assumptions of the rules is, the bad guy has accomplices. Therefore, you want to grip your opponent in such as way as to be able to control their shoulders and hips to prevent them from punching and kicking you, and to use them as a body shield, keeping them between you and their accomplices. This is the traditional grip with on hand on the lapel and one hand on the sleeve. obviously, in a Judo match it is just you and your opponent, but this is still the idea. If you have a non-standard grip (e.g. two sleeves or both hands on one side of the body) you must be using it to attack. As long as you are actively setting up and attacking you may maintain an alternate grip. If you find yourself in a position where you can no longer attack, you must switch back to a traditional grip.
In ground work you, in a real fight, you do not want to be on the ground longer than you have to, and you want to maintain the ability to stand up when necessary. As long as there is progress being made, the referee will allow the match to continue in ne waza (ground work).
As the "good guy", your goal is to finish the fight as quickly as possible with a technique that would win the fight in a real situation.
Throwing your opponent, with a recognizable Judo technique, from their feet to their back with speed, force, and control. Control must be maintained all the way through the landing for a score to be given. If the referee deems your throw to be lacking in one or more of the four areas, but still good enough for a score, you are given a score of waza ari, which translates to "with technique". This score by itself isn't enough to win the match.
Pinning your opponent for 20 seconds. While pinning your opponent's back should be generally toward the mat or one of their shoulders must remain in contact with the mat and you must remain free from being entangled by their legs. If you pin your opponent for more than 10 seconds, but less then 20, you earn a score of waza ari (with technique).
If allowed in the division you are fighting in, with a strangulation technique.
if allowed in the division you are fighting in, with a joint locking technique against the elbow.
With a combination of two attacks which were deemed good enough for a score, but not good enough for an ippon (one point). The second waza ari is raised to ippon (one point). The referee will call, "waza ari awaseti ippon".
Being overly passive (not attacking). Remember, you are trying to finish the fight as quickly as possible before the bad guys accomplices show up to help. You don't have time to be passive.
Holding a single sided grip without attacking. While great for throwing, you lack control of your opponent if they were striking.
Being overly defensive (stiff arming, bent over posture). Remember, you are trying to finish the fight as quickly as possible before the bad guys accomplices show up to help. You don't have time to just block your opponent from attacking. You need to attack.
Attacking or blocking your opponents legs while one or both opponent are standing. This rule was created in an effort to get the contestants to stand up where they would be able to defend themselves if their opponent was striking.
Attempting to apply a joint lock or strangulation while one or both contestants are standing
Doing these will disqualify you from the match, but you can continue the tournament if the loss doesn't eliminate you.
Receiving a third shido (minor penalty) is awarded as hansoku make.
To “dive” headfirst, onto the tatami by bending forward and downward while performing or attempting to perform techniques such as uchi-mata, harai-goshi, kataguruma etc. it is forbidden to somersault forward when uke is on the shoulders or the back of tori.
Head defence, to ensure that judo has as little trauma as possible, if uke attempts voluntarily to use the head with any movement which is dangerous for the head, neck or spine, for defence and to avoid landing in/escaping from a score he shall be penalised with hansoku-make.
Special attention will be given to situations where tori attempts to throw his opponent during tachi-waza with, for example, seoi-otoshi, seoi-nage, sode-tsurikomi-goshi with the grip on both sleeves and koshi-guruma with both grips on the collar and uke makes an involuntary head defence.
These are examples and this situation can occur with other throwing techniques. In this situation there is no penalty for either tori or uke.
Doing these will eliminate you from the tournament. Yes, even if you were in multiple divisions.
1. To apply kawazu-gake (to throw the opponent by winding one leg around the opponent’s leg, while facing more or less in the same direction as the opponent and falling backwards into him).
Even if the thrower twists/turns during the throwing action, this should still be considered “kawazu-gake” and be penalised. Techniques such as o-soto-gari, o-uchi-gari, and uchimata where the foot/leg is entwined with opponent’s leg will be permitted and should be scored.
The application of kani-basami and do-jime (applying leg scissors to the opponent’s trunk, neck or head (scissor with crossed feet), while stretching out the legs) be penalised with hansoku-make.
To apply kansetsu-waza (ashi-garami, ude-gaeshi etc.) anywhere other than to the elbow joint.
To fall directly to the tatami while applying or attempting to apply techniques such as ude-hishigi-waki-gatame.
Applying kansetsu-waza or shime-waza in tachi-shisei with a judo throwing technique with be penalised with hansoku-make.
Uke, when behind tori, cannot reap tori’s leg or legs from the inside.
To make any action this may endanger or injure the opponent especially the opponent’s neck or spinal vertebrae.
Intentionally fall backwards when the other athlete is clinging to his back and when either athlete has control of the other’s movement.
To lift the opponent off the tatami and forcefully push him back onto the tatami without a judo technique.
To disregard the referee’s instructions.
To make unnecessary calls, remarks, or gestures derogatory to the opponent or referee during the contest.
To wear or to have inside the judogi a hard or metallic object (covered or not).
Any action against the spirit of judo (this includes anything that can be described as anti-judo, for example being in the lead and, in the last seconds of the match, leaving the competition area to prevent the opponent from taking grips) may be punished by a direct hansoku-make at any time in the contest.
The original Judo gi was shorter in the sleeves and pant legs, more closely matching the traditional Japanese Kimono of the day. As Japan adopted more of the customs of the West, and as Judo spread throughout the world, the sleeve and pant length was increased to match that of a business suit. Today the gi sleeves should fall comfortably to your wrists and the pants should hang to the tops of your feet. Since you are providing the equipment for you partner to grip, and your partner is providing the equipment for you to grip, there should be sufficient slack in the gi throughout the arms for your partner to take a grip. The material should be sturdy enough to stand up to being pulled on, but supple enough to be gripped. Your gi should be clean and in good repair. Your belt should be properly and securely tied around your waste, and should represent the color of the official Judo rank you hold.
The competition area consists of a safety zone, which the players should generally avoid, and the contest area. If you and your partner enter the safety zone as the result of attacking action, the referee will allow the action to continue as long as it is safe for you and your partner. Forcing your partner into the safety zone, or entering the safety zone without attacking action will result in a penalty.
When entering the contest area, you and your opponent will bow into the safety zone. You will then bow into the contest area as you exit the safety zone. As you and your opponent approach each other toward the center of the mat, you will bow to each other as a show of respect and take one step forward to let the referee know you are ready to being the contest.
At the end of the contest, when the referee awards the match, you and your opponent will take one step backwards and bow to each other. You will each bow out of the contest area and then bow out of the safety zone as you bow off the mat.