Hiza-soto-muso (膝外無双), the outer knee twist-down.
Said: hee-ZAH SOH-toh MOO-soh

At a glance
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Nage-waza (throwing techniques), Te-waza (hand techniques).
Also known as: soto-muso (sumo) - The sumo twist-down this judo form borrows its name and shape from..

About
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The outer knee twist-down, borrowed from sumo's soto-muso: one hand leaves its grip to press the outside of uke's knee, and the other hand and chest twist them down backwards over the blocked leg. A rarity of international contest footage rather than the Kodokan classification, documented here under the name the video libraries use.

Where this technique is not allowed
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Penalised in competition: the blocking hand works directly on uke's leg, which current IJF rules answer with a shido. Outside contest the technique is unaffected.

Under contest rules
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The blocking hand works on uke's leg, which draws a shido.
Source: Sport and Organisation Rules of the International Judo Federation: refereeing rules, 2026 edition, Article 18.1.2.

Key points
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1. Break the balance to the rear corner before the hand goes to the knee
2. The palm blocks the outside of the knee; the block holds still while the body turns
3. Twist with the remaining grip and your chest, steering them down over the blocked leg

Demonstrations
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Akita Judo: Hiza-soto-muso https://www.youtube.com/watch?v=L_JQ_MnU6M8

In combinations, counters and transitions
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None yet.

From Waza Book: https://wazabook.com/techniques/hiza-soto-muso/