Gyakuzuki no tsukkomi teaches rotational penetrating movement while avoiding. In contrast to regular gyakuzuki, the upper body is leaning forward and there are two center lines at play instead of one. The difficulty of this technique, is to shift the center to the side at the last split second, while directing your full weight into the knuckle striking straight forward. Make sure a forward movement is never outside of your own shoulder line, as this would weaken the punch.