I'm the brown guy. I went to the beach this weekend and there was a guy doing gainers into the water at china walls. He sprinted forward toward the edge of the wall, and jumped outward and forward while at the same time generating a backward torque to rotate his body backward, while moving forward into the water. It was pretty cool. He jumps outward and while hes in the air he pulls his knees to his chest to begin the backward rotation. Then he lands in the water and the water exerts a force on him to stop the downward motion. This force results in a change in momentum , constituting an impulse. Since it takes so much time for him to stop moving downward in the water, the force is proportionally small.