Son assault demesne, or "his own first assault," is a form of a plea to justify

Justification (jurisprudence)

Justification in jurisprudence is an exception to the prohibition of committing certain offenses. Justification can be a defense in a prosecution for a criminal offense. When an act is justified, a person is not criminally liable even though his act would otherwise constitute an offense. For...

 an assault

Assault

In law, assault is a crime causing a victim to fear violence. The term is often confused with battery, which involves physical contact. The specific meaning of assault varies between countries, but can refer to an act that causes another to apprehend immediate and personal violence, or in the more...

 and battery

Battery (crime)

Battery is a criminal offense involving unlawful physical contact, distinct from assault which is the fear of such contact.In the United States, criminal battery, or simply battery, is the use of force against another, resulting in harmful or offensive contact...

, by which the defendant

Defendant

A defendant or defender is any party who is required to answer the complaint of a plaintiff or pursuer in a civil lawsuit before a court, or any party who has been formally charged or accused of violating a criminal statute...

 asserts that the plaintiff

Plaintiff

A plaintiff , also known as a claimant or complainant, is the term used in some jurisdictions for the party who initiates a lawsuit before a court...

 committed an assault upon him, and the defendant merely defended himself. When the plea is supported by evidence, it is a sufficient justification, unless the retaliation by the defendant were excessive

Excessive Force

Excessive Force is a musical side project started in 1991 by Sascha Konietzko of KMFDM and Buzz McCoy of My Life With the Thrill Kill Kult.-History:...

, and bore no proportion to the necessity

Necessity

In U.S. criminal law, necessity may be either a possible justification or an exculpation for breaking the law. Defendants seeking to rely on this defense argue that they should not be held liable for their actions as a crime because their conduct was necessary to prevent some greater harm and when...

, or to the provocation received. Character evidence

Character evidence

Character evidence is a term used in the law of evidence to describe any testimony or document submitted for the purpose of proving that a person acted in a particular way on a particular occasion based on the character or disposition of that person...

that the plaintiff was noted for quarrelsomeness is generally admissible where an answer of son assault demesne is filed.