(a) A person may, subject to the provisions of paragraph (b) of this section, use physical force upon another person when and to the extent he reasonably believes such to be necessary to defend himself or a third person from what he reasonably believes to be the use or imminent use of unlawful force by such other person, unless:

    (1)    The actor was the initial aggressor; except that in such case his use of force is nevertheless justified provided:

        a.    He has withdrawn from the encounter and effectively communicated such withdrawal to such other person but the latter persists in continuing the incident by the use or threatened use of unlawful force; or

        b.    He is a law enforcement officer and as such is an aggressor pursuant to section 563.046, RSMo.; or

        c.    The aggression is justified under some other provision of this division or other provision of law.

    (2)    Under the circumstances as the actor reasonably believes them to be, the person whom he seeks to protect would not be justified in using such protective force.

    (b) A person may not use deadly force upon another person under the circumstances specified in paragraph (a) of this section unless deadly force is authorized under state or federal law.

    (c) The justification afforded by this section extends to the use of physical restraint as protective force provided that the actor takes all reasonable measures to terminate the restraint as soon as it is reasonable to do so.

    (d) The defendant shall have the burden of injecting the issue of justification under this section.

(Code 1964, § 7.650)

     State law reference(s)--Similar provisions, RSMo. § 563.031.