PLEASE understand that I am . . not . . a lawyer, nor do I play one
THEREFORE, NOTHING I say here should be considered legal advice!
It's worth exactly what you paid for it . . nothing.
Self defense is a process of countermeasures that can be used to maintain your well-being against attack/harm from another.
The very best self defense is avoidance!
If you are not involved in an incident, you do not need to take action against it.
Self defense can not use force stronger than the threat.
More simply you can not use deadly force to counter a non-deadly force threat.
The "right of self-defense" is the right of a person to use reasonable and appropriate force to defend one's own life and well-being; including the use of deadly force, if necessary.
Early Roman Law theories make no distinction between defense of the person and defense of property. This builds on the principle of dominium where any attack on the members of the family or the property it owned was considered a personal attack on the pater familias - the male head of the household, sole owner of all property belonging to the household, and endowed by law with dominion over all his descendants.
The right to self-defense is phrased as the principle of vim vi repellere licet ("it is permitted to repel force by force") in the Digest of Justitian (6th century).
The Universal Declaration of Human Rights states:
No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honor and reputation. Everyone has the right to the protection of the law against such interference or attacks.
It follows then that laws must simultaneously criminalize aggression resulting in loss or injury, but decriminalize qualitatively identical violence causing loss or injury because it is used in self-defense. More simply, violence in defense of person is appropriate because it takes right from the criminal and returns it to the owner/victim.