A punches B
B beats up A
A ceases fighting
B does not stop
by not stopping B has become the aggressor
A can now attempt a self-defense justification on lethal force to stop B's assault.
-This does not absolve A of the initial criminal assault however, there is simply now 2 criminal assaults that have occurred; one by A and one by B.
It is a legal parallel to the person who defends his home or family or business from an intruder. If you break into my house and I let you have it with both barrels of Ole Betsy, then I am legally justified. However, if I reload and then shoot you again while you are down, I have committed murder (that is why having a large capacity magazine is great, no reload window).
There have been some criminal cases of this nature, and many civil ones.
For legal justification of self-defense, the defender -- in the example we've been debating, person A after the tables have turned on them in a fight -- must have either attempted to remove themselves from the situation and been prevented from doing so, or felt they had no other option other than to respond with deadly force. If A initiates contact, that removes the idea that A had no other option but deadly force. You cannot start a fight, lose that fight badly, and then justifiably kill the other person. Again, I ask you to cite any case you can find where this exact scenario occurred and I will cede the point to you. As I understand the law, though, your scenario is not justifiable homicide no matter how you look at it.
