All combat sports are very strict with blows to the back of the head and neck. You only have to see what happens when there's an accidental strike to this area to know how lethal things could be (e.g. that TUF 5 fight with Lauzon and Miller). So what are we talking about ? Can you kill someone easily with a blow to back of neck ? Paralysis ? or just disorientation ? Would you strike to this area in a street fight ?