from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
SON ASSAULT DEMESNE, pleading. His own first assault. A form of a plea to
justify an assault and battery, by which the defendant asserts that the
plaintiff committed an assault upon him, and the defendant merely defended
himself.
2. When the plea is supported by evidence, it is a sufficient
justification, unless the retaliation by the defendant were excessive, and
bore no proportion to the necessity, or to the provocation received. 1 East,
P. C. 406; 1 Chit. Pr. 595.