There is no good empty-handed defense against a knife

Knives are extremely dangerous and there is no good way to defend against one empty-handed; a genuinely intent attacker will not brandish the knife but walk up close, grab you, and repeatedly pump the blade in, so you feel it before you see it, and the closest viable method (the STAB system) involves using clinch skills to control the weapon arm via a two-on-one while accepting you will likely get stabbed.