What is justifiable self defense though?

I'm guessing that if someone walked up and punched you in the face that you wouldn't be allowed to shoot them dead, I would imagine/hope that you would have to answer some serious questions if that happened.

But when is it acceptable to pull a gun? hows about if someone is waving a baseball bat around? would you be expected to run or would the courts look at that as a justifiable reason to use your gun?

Also would you be expected to try and incapacitate them (ie shoot them in the leg) or is 'self defense' classed as just self defense regardless of the outcome or severity.

Hows about you @El Kabong what would be your limit? would you be willing to take a good hard kicking before pulling your gun (obviously I'm talking about out on the street and not someone breaking into your home)