Sumi-gaeshi (corner reversal) is a sacrifice throw from the fourth group of the gokyo. Tori drops onto the back, lifts the inside of uke's thigh with the instep and throws uke diagonally over the shoulder. It is the natural weapon against a bent-over opponent who defends with stiff arms and a low head.
How it differs from other sacrifice throws
It is a ma-sutemi-waza, a technique where tori falls straight onto the back. Its neighbors in that family are tomoe-nage, ura-nage and hikikomi-gaeshi. It appears in the nage-no-kata right after tomoe-nage, and in the fourth group of the gokyo. For the bigger picture, see our overview of nage-waza.
The difference from tomoe-nage comes down to two points. Direction: diagonally toward a corner rather than straight over the head. Contact: the instep under the thigh rather than the sole on the belly.
The ideal opponent for sumi-gaeshi
Modern judo serves up plenty of chances. Picture an opponent in jigotai (defensive posture), knees bent and chest leaning forward onto your shoulders. The weight is already in front. All that is left is to take it.
The matching grip is one hand over the shoulder, on the back or the belt, with the other hand on the sleeve. In opposite stance, the cross grip on the back is very common. That control of the back stops uke from standing up as you drop.
How to do sumi-gaeshi
Entry. Tori steps the left foot between uke's feet, close in. Both hands pull uke in and down, which exaggerates the bent posture.
Placement. The right instep slides against the inside of uke's left thigh, just above the knee.
Drop. Tori falls onto the back with the hips near the left heel, underneath uke.
Throw. The right leg lifts the thigh. The hands pull uke diagonally over tori's right shoulder and uke takes a forward rolling breakfall.
Tori's fall has to be tight against uke. It is the same rule as in tomoe-nage, and the same mistake causes most failures.
Where it goes wrong
A foot that pushes instead of lifting lets uke simply step back while tori stays on the mat. If tori's back lands far away, the leg loses its leverage. If the pull stops during the fall, uke catches himself on his hands.
There is also a reading error. Against an upright opponent, sumi-gaeshi almost never works. It needs uke already bent over. If you have to create that posture yourself, pull down several times before you go in. Uke gets used to resisting upward, and then gives way.
Counters and risks
When uke feels the drop coming, uke can flatten forward onto the knees and get out of the circle. Stepping over tori's leg is another way out. Like any failed ma-sutemi, a missed sumi-gaeshi leaves tori on the back with uke on top, which is a weak spot against someone good on the ground.
Referees also penalize false attacks. A half-hearted attempt to break the standing rhythm soon costs a shido.
Ground follow-ups
A clean sumi-gaeshi leaves tori in position to roll on top of uke. You often finish seated or mounted, ready to pin. When uke lands face down, tori ends up on the back, with hadaka-jime or a turnover within reach.
In Brazilian jiu-jitsu, the same movement is used as a sweep from butterfly guard or open guard. The hooks under the thighs go by another name there, but the mechanics are the same. For the full comparison of the two sports, see BJJ vs judo.
Train it on the ground first
Start on the mat with tori on the back and uke kneeling above. Tori places the instep and sends uke over diagonally. Then uke stands bent over while tori sits down and throws. Then add movement, against a uke pushing from a low posture.
Our view: sumi-gaeshi is the best answer to opponents who defend folded in half. Judoka who have it in their arsenal stop suffering that blocked style of judo. Learn it early, along with its ground follow-ups.