The Sumi-otoshi (Corner drop) Waza begins in the same manner as the Uki-otoshi (Floating drop), in that the opponent is induced to take a step back, with the Waza then being applied in the moment when he brings that foot forward again.
From the natural posture, Tori (Player executing technique) grasps Uke (Player receiving opponent's attack) mid-sleeve area, as deeply as possible. Tori then aggressively forces Uke back in order to induce him to then bring a foot forward in retaliation.
The force with the retaliatory foot is brought forward at this time is generally proportional to the force of the aggression which was applied. At the moment Uke steps forward, Tori extends his leg to act as a fulcrum. Tori pulls Uke in the direction of the grasped sleeve, pulling his Center of gravity against the extended leg. At the same time, Tori other hand (which is grasping Uke collar) pulls Uke chest upward.
Uke body then rotates over Tori fulcrum leg and he falls to the floor.
The best time to apply this Waza is when the opponent moves forward in an aggressive attack, or when he stops an attack and moves backward. Although this Waza appears to be executed by hand work alone (thus earning it the "air throw" name), subtle body motion is also required in order to destabilize the opponent, with the opponent being thrown by the resulting force. Therefore, this Waza is executed using the entire body.