Hara to hara. You move your opponent in sync with you. You control the opponent with your hips via his hips with your legs. Look up Glima and Scottish wrestling on Youtube for example of this. That is what is at the core of these two sports. It is harder to see it happening in Sumo in comparison to Glima or Scottish wrestling.
What if he doesn't want to move with you? Would the dance be over? Is sumo a form of Japanese dance?