Many citizens have a misconception about defending themselves and the legal consequences attached to the act of self defence. The misconception seems to focus on the belief that if a defender strikes the attacker they will also be charged with assault. This misconception, sad to say, leads to many citizens giving thugs the green light to either push them around or hurt them because the belief is:
The misconception described above, unfortunately, gives the criminal permission to commit crimes based on their belief that the victim will comply to their demands. The bottom line is you do have the right to defend yourself, using reasonable force or force that is adequate to stop the attack from continuing. For example, if the thug is unarmed and attempting to strongarm you out of your hard-earned money and property then you can defend yourself with enough force to allow you to escape to safety.
However, should you be facing an armed thug then, depending on the situation, it might be wise to comply. Certainly, citizens shouldn't casually decide to resist a mugger unless they have made a careful assessment of the threat and are confident they can repel the thug or, better yet, escape/run away from the situation without having to fight. Only the defender can make the choice of what to do.
REMEMBER! You will likely get charged with assault if you go beyond using reasonable force to defend yourself. For example: if you are convinced a thug is about to harm you and you hit him/her once and they are stunned or momentarily dazed, allowing you to escape - that's okay. However, if, in this same scenario, you opt to hit the thug once or twice more instead of escaping the situation to safety you may be charged with assault, especially if you have injured the thug. The first instance was reasonable force, the second is excessive force.
Mitigating factors such as size, maturity and age differences, the attacker's mindset, etc will likely be considered in the amount of justified force used in self defence.