Kuzure-yoko-shiho-gatame (崩横四方固), the modified side four-quarter hold.

Osaekomi-waza (hold-downs).

About
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The side four-quarter hold with one of its grips broken: an arm controls uke's near arm or head instead of the standard neck-and-leg pair. The form the hold usually takes in live groundwork, where uke never lets the textbook grips settle.

Step by step (standard right-handed form)
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1. Take the side four-quarter position at your partner's right side, chest on chest at right angles.
2. Instead of both standard grips, thread one arm under their head or trap their near arm against your side; the other hand grips the belt or far leg as usual.
3. Keep your hips low or knees tucked in tight, leaving no space beneath you.
4. Press the chest down and keep your head low on the far side.
5. As they work an arm free or turn, flow between this and the pure form, the chest never lifting.

Key points
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1. Same chest pressure as the pure form; only the grips change
2. Control the near arm or the head with the freed hand
3. Switch between forms as they work their arms free

Receiving it
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Side control weight, but with your near arm or head controlled instead of the textbook grips, so your usual first escape is already answered. Hunt whichever side is least controlled: bridge and turn towards them, work an elbow inside, and change directions rather than repeating one escape. Tap clearly if you need to stop.

VI judo notes
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In live groundwork the textbook grips never settle, and this broken form is what your hands actually find. Keep chest contact as the constant and let the grips change underneath it: an arm threaded under the head, or their near arm trapped at your side, whichever is there. The chest is also how you are reading them, so it stays down while you re-grip.

From Waza Book: https://wazabook.com/techniques/kuzure-yoko-shiho-gatame/