It means that the feet of the other person leave the ground in such a way that they have no control or certain knowledge of what has just happened. As they come down you can whack them.
John Kells told us that we must attack the root from the outset.
In the picture below you can see the person's feet coming off the ground. We practised lots of uprooting exercises so that the body/mind set required would be hardwired into our approach to the Form.
