Kuzushi is often mentioned as one of the key elements in performing techniques, but kuzushi goes beyond mere taking the aite’s physical balance.
The concept of kuzushi in Japanese martial arts are similar, although each of them describe it or focus on different aspects. In kenjutsu and kendo, the unbalancing is discussed in terms the tip of the sword or “剣先” (kensen). In kenjutsu the “正中線”(seichusen) and various other places of point the tip of the sword are used to control and unbalance the aite. This also applies to jojutsu and bojutsu, with the use of the tip of the bo pointed along certain lines or used to control or judge the lines. Also various kamae are also used for unbalancing and controlling the aite. In jujutsu/taijutsu kuzushi is discussed in terms of direction of balance and controlling certain space to allow for a throw. Also, various kamae are used to set initiate and control of the directions of balance.
Kuzushi is primarily about splitting the aite’s lines of strength and power, while moving into a place where you are more balanced and have more “strength” (structural strength). An easy way to think about kuzushi is to think about moving yourself or some attack through their weakest lines while lining up your stronger lines along those lines. Or more simply, move where they are weakest, slowest, and can’t regain balance. To off balance an aite effectively requires that one understands their own balance through an attack and defense. It also requires that one understands where their lines of force are directed. These lines of force are understood as the relation between the joints and the direction of force they can impose on an attack and defense. This is also important for cutting quickly and effectively, if your arms and elbows are out of line with your hips and legs you will oppose yourself when you cut. As your force is spread out over a wide angle. This is the difference between a flash light and a laser beam when it comes to cutting.
Balance can only be effectively broken when the other person can’t fight effectively or easily regain balance. This requires a type of training that most don’t know where to look. Examples can be found in Kendo and Judo. In Kendo they have Kakari-geiko (掛稽古) and Ji-geiko (地稽古) which are types of unscripted practice, in the Bujinkan we have basic randori and some kata that require unscripted attacks. In judo, they focus more on randori than most traditional schools as most of the practice is geared towards competitions and matches. Non-compliance in training techniques is a mainstay of the martial arts. It shouldn’t be neglected in our practice, but it also shouldn’t take over the overall practice either like it can in both kendo and judo. However, it depends on the relationship between the uchidachi and shidachi to have an effective practice your uchidachi ought to be better than you.
Also, the mental balance can be taken to unbalance the body. Unbalance the mind and you can unbalance the body. This can be done with varying tempo or capturing the aite’s attention and have them focus on things that lead their balance towards your stronger lines and onto their weaker lines. In kendo, this can be done with varying kinds of seme. Also, it can be done with feints and direct attacks alone obvious defensive lines to open up the weaker lines.
Since this subject is extremely difficult to talk about effectively.