An affirmative defense to a criminal charge and it is the use of reasonable force to protect one’s self from an another person who appears to be attempting to cause that person harm. Reasonable force must be used, generally equal force but not greater to meet an attack.
Law Dictionary – Alternative Legal Definition
In criminal law. The protection of one’s person or property against some injury attempted by another. The right of such protection. An excuse for the use of force in resisting an attack on the person, and especially for killing an assailant.