Grappling is being approached just like Aiki. The fundamental principles of grappling are balance and center.
The basic activity of grappling is the pin which is really just lying on top of your partner. Depending on the sport or situation the person on top holds the person on bottom long enough to demonstrate control, or the person on top uses the position of control to injure the person on bottom. The person on top must maintain balance and control.
The person on bottom has to disturb the balance and control of the person on top to attain the top position or injure the previously controlling partner. There are a few basic ways of doing this. This system uses about four ways of breaking the top partners balance and attaining the top position. These are analogous to the off balance moves that are the basis of Aikido.
When standing the partner falls when balance is lost. On the ground the partner loses the top position.