In general, to defend yourself against a physical attack, you must do whatever it takes to free yourself from the assailant and run to safety. Ideally, your defense will be swift and effective thus minimizing the time you are wrestling or grappling with the perpetrator. In essence, you must use the minimum amount of force necessary to prevent an assault from escalating any further to ensure your own wellbeing. According to Joan M. Nelson in her book Self-Defense: Steps to Success, this concept describes the ethic of least harm. The ethic of least harm is defined by the commitment to using the least damaging or punishing techniques necessary to deter an attacker while still doing whatever is required to ensure your own safety.
Some people believe that the ethic of least harm unfairly holds the victim to a higher moral and ethical standard than the perpetrator and that the perps should "deserve whatever they get." Those same people believe that the aggressor should get a few extra punishing blows to the groin to teach him a lesson or two. However, those extra finishing maneuvers against the assailant leaves the victim within close proximity of the attacker thus leaving the victim at risk of his own safety longer than necessary. By repeatedly attacking the attacker, you run the risk of making him meaner such that he will react against you with greater violence.
Regardless of legal or ethical considerations, for practicality it simply makes sense to exert the minimum amount of force needed to obliterate a confrontation and retreat as quickly as possible to call police. This includes choosing the least minimum lethal response.
Once you choose a method necessary to use on your attacker, react quickly and efficiently. Defend yourself with whatever means is reasonable and necessary. Do so in order to stop the assault and not to kill the attacker.