I believe my definition of WC center-line is much easier to be understood in general. When you are on your opponent's side door (blind side), you can guide his leading arm to jam his back arm. Since you have to use one hand to guide his leading arm, you have 1 free arm left to attack him. IMO, this is the major difference between CMA and boxing. - In boxing, you have 2 free hands and your opponent also has 2 free hands. - In CMA, you want to have 1 free hands and your opponent has no free hands. This idea is also the same as the difference between Judo and Chinese wrestling. - In Judo, both you and your opponent want to have 2 hands to grab on each other. - In Chinese wrestling, you want to have 1 hand to grab on your opponent while your opponent has no hand on you. In the following clip, A's left hand controls B's left leading arm. A's right hand punches at B's face. B's right hand is jammed by his own left arm and cannot reach to A.