The whole purpose of self defense is to protect yourself against the attacker and go back home safe. When you fight for self defense, you are not there to prove something or show off. Anyway, when your life is in danger, that's not a show.
Let's get thing real. The attacker might not come and attack you instantly. Sometimes the attacker talk to you in a rude way before attacking you. The moment you feel something is wrong, and I think when you are in a situation like this, you will get the signal, focus and be aware of your surroundings.
Where you are, you are alone or there are other people around you; all things help you set up self defense strategy. If the attacker starts attacking you, and you do not have any other options, you have to be proactive.
You can stop the attacker intercepting his strike. When the attacker punches you, you can kick to his leg to stop him and then you can for another strike. Or, you can go out of there.