Kuzushi, (崩し), is the Japanese term for controlling the opponent's balance and centre of gravity as a preparation for throwing techniques.
Kuzushi in martial sports
Kuzushi in martial sports such as Judo is dependent upon grabbing the opponent, pushing or pulling and creating the appropriate reaction for a specific throw. Other Martial sports such as Sumo and Wrestling might use non direct Kuzushi that necessitates an acute feel for timing in order to use the opponent's momentum.
Kuzushi in martial arts
Kuzushi in other martial arts, such as Aikido or Ninjutsu may use other principles apart from pushing and pulling. In Aikido the practitioner might use the opponent's momentum as a kuzushi and thus the Kuzushi principle in Aikido mainly involves advanced timing.
Some of the kata and the Randori in Ninjutsu make use not only of timing or push - pull action but of Punches and kicks. The opponent's centre of gravity is maneuvered into place by the precise action of hitting a limb and using the reaction thus created.
Video of hitting for kuzushi in Ninjutsu
Video of different types of Judo push-pull kuzushi