Is self-defence to rely on to run? How do you look?

What calls self-defence? Take a knife when hellion to you when, you cannot strike back, because harm has not happen, he may be to frighten hiss you. . Wait for hellion to be inserted into your body with the knife, you also cannot strike back, because harm has stopped, he may stop stay a hand. Pull out when hellion the knife is you cannot strike back more, because harm has ended, he may not want to give you one knife again. Wanted you to strike back only, possible meeting offends criminal law. What will be inserted into your body with the knife when hellion only is flashy, you should judge essence of life quickly to allow to strike back, and should shoot dead a life, this ability calculates self-defence.