With your right hand which is holding the collar, bear down with all your weight over the leg you are taking away. Your left hand should contribute to this action by pushing your opponent's arm and upper body in the same direction. One important point to remember is the direction of the throw. You are throwing your partner backwards and down. This means that when you are actually doing the throw you should be moving in those directions too (forward and down).
If you are very fast and catch your man completely on the hop with his legs spread wide he will collapse backwards instantly. This is not often possible. It is usually necessary to complete the technique by bearing down on the opponent's left shoulder all the way to the mat. It is not necessary to fall on the opponent. Your hands still holding your partner's jacket pin him to the ground and should be used for preventing your body crushing into his. Note the position of my head and right shoulder. After I have got the man toppling backwards it is necessary to guard against an effective counter for this throw.