http://smashpass.blogspot.com/2007/05/20-fundamental-moves-of-jiu-jitsu.html“The mechanics are very simple. It consists of breaking the adversary’s posture with a kick to the armpit. In order to perform this kick, one must make a slight change in the angle of the hips, so that they create a better lever. As you achieve this break of posture, the opponent’s lower body gets lighter, enabling the reversal with the grip on the pants, on the same side as the leg of the kick.
The other detail is the positioning of the base-foot; it must be fixed on the ground and close to the opponent’s shin. By raising the foot, the lever is lost. There is a variation, putting that very same foot on the foe’s hip. The secret to this sweep is the timing, for if you just execute it, the adversary will be rigid and strong; so it’s necessary to feel they are relaxed and surprise them right then. Another advantage of this sweep is that the opponent doesn’t feel comfortable moving, which makes them, in their anxiety, leave room for other attacks.”