This is an Aikido Randori, neither is uke or nage, both are trying to throw or submit the other person. The guy with the knife is also trying to cut or stab. The action starts once there is a firm Katate dori grab made, and goes to submission, throw, cut/stab or a brake. The knifer is can switch knife hand or brake free any way he can.
www.centralvalleyaikido.com
