Learn ko-soto-gari, the minor outer reap in judo: kuzushi, heel and timing. Beginner-friendly and honest, with breakfalls and a supervised partner.
The honest answer: ko-soto-gari is a quick backward throw that pulls your partner's heel away from the outside while you push him backward and sideways with your upper body. It looks smaller than o-soto-gari and is therefore a popular entry into outer reaps. The German Judo Federation assigns ko-soto-gari to the basic programme and lists it together with ko-soto-gake in one line [1].
And here comes an honesty you rarely read: the DJB itself writes that the distinction between ko-soto-gari and ko-soto-gake is hardly manageable for beginners. Therefore only one of the two techniques or a mixed form is expected, as long as the action is coherent in itself [1]. So you do not have to master every subtlety of naming to practise it. How long it takes until the reap lands is individual. That is a practical rule of thumb, not a study.
One hand on the sleeve, the other on the lapel. Upright, knees slightly bent, eyes forward. Milestone: you lead Uke evenly to the side and backward without tipping yourself.
With pull and push you bring Uke into the rear corner, his weight on one heel. That is the moment in which the reap can work. Milestone: Uke feels the shift and can no longer lift the leg.
You place your standing leg close next to Uke's foot, knee bent, upper body upright. Milestone: you reach the position in one step without Uke stepping away.
Without a partner you practise the sole of the foot at the imaginary heel area: a short pull in the direction of the toes, not kicking into the air. Milestone: 10 clean repetitions per side.
With a partner you practise push and reap in one flowing motion. Only with your coach's approval do you throw for the first time and accompany Uke with the pulling hand to the landing. In competition an ippon requires speed, force, landing on the back and controlled landing [2]. Milestone: Uke lands on his back, chin to chest, hands slapping.
As with any throw: being thrown is the most common injury mechanism in judo, most often affecting knees, shoulders and fingers [5]. With outer reaps the knee of the person thrown is added: in a survey of 43 cruciate ligament cases in judo, they occurred clearly more often when the stances were different (kenka-yotsu, e.g. right-handed against left-handed), than with matching stances, and more often when one was attacked than when one attacked oneself [3]. That means: with mismatched stances in training reap especially under control, never to the knee. A review also found a hint that fatigue worsens breakfall skill [6]. So no throwing drills when you or your partner are exhausted. You only throw partners who can do ukemi securely, on tatami and under supervision. This guide explains and motivates, it does not replace supervised training.
See ko-soto-gari as an answer, not a question: it works especially well when Uke is just attacking or stepping back. At the 2013 World Championships, asymmetrical starting positions (different stances) produced more counter-attacks and backward-direction attacks than expected [4]. That is not a statement about ko-soto-gari alone, but a hint that timing against the partner's movement is a big lever. Whoever waits until the partner moves rarely throws against resistance.
Also practise staying alert right after the throw: if Uke stays down, you accompany him calmly; if he rolls away, you are already in the next step. That is everyday judo, but practice, not a study.
Both aim at the leg from the outside. The difference lies in how the foot technique is executed. The German Judo Federation regards the distinction as very difficult for beginners and requires only one of the two techniques or a functional mixed form [1].
Yes, it belongs to the DJB basic programme [1]. What matters: secure ushiro-ukemi, an attentive coach and controlled practice.
Yes, as a judo technique. Kicks against leg or ankle without a technique, grabbing the legs and hooking without an immediate attack are forbidden [2].
You can practise the foot movement alone, but not the throw. You recognise the moment of the weight shift only against a moving partner.
O-soto-gari reaps the whole leg from the outside-back and uses your body weight strongly. Ko-soto-gari aims briefly at the heel and lives from the moment Uke's weight sits there. Both need kuzushi backward and sideways; the German Judo Federation lists both in the basic programme [1].
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