A.R.S. § 13-406: Justification; defense of a third person

A person is justified in threatening or using physical force or deadly physical force against another to protect a third person if, under the circumstances as a reasonable person would believe them to be, such person would be justified under section 13-404 or 13-405 in threatening or using physical force or deadly physical force to protect himself against the unlawful physical force or deadly physical force a reasonable person would believe is threatening the third person he seeks to protect.