Missouri Approved Instructions–Criminal (MAI-CR) 4th
406.08 JUSTIFICATION: USE OF PHYSICAL FORCE IN DEFENSE OF THIRD PERSONS
One of the issues (as to Count _____) (in this case) is whether the use of physical force by the defendant against [Identify victim.] was lawful. On the issue of defense of another person (as to Count _______) (in this case), you are instructed as follows:
In this state the use of physical force (, including the use of deadly force,) to defend another person is lawful in certain situations. [Select the appropriate paragraphs. Omit brackets and number.]
[Use the material in  only if there is evidence that the person being defended was not justified in using physical force in self-defense and there is evidence that the defendant was aware of this. Omit brackets and number.]
 However, a person cannot use physical force to defend another person against physical force if under the circumstances as he reasonably believed them to be, the person he seeks to protect would not be justified in using physical force to defend himself. [Insert brief description of the basis why the person being protected would not be justified in using physical force to defend himself. See Notes on Use 5 for examples. If more than one option is used, they should be connected with “or.”] If, under the circumstances as a person reasonably believed them to be, the person he seeks to protect (was the initial aggressor (and had not withdrawn)) (was being arrested by a law enforcement officer) (was (attempting to commit) (committing) (escaping after committing) [Insert name of forcible felony.]) ([other basis for lack of justification]), then he is not entitled to use physical force to defend the other person.
[Use the material in  in all cases. Omit brackets and number. The parenthetical term “non-deadly” should only be selected if the material in  is used.]
 In order for a person to lawfully use (non-deadly) physical force in defense of another person, he must reasonably believe that physical force is necessary to defend the person he is trying to defend from what he reasonably believes to be the use or imminent use of unlawful force and he can only use physical force to the extent that he reasonably believes is necessary to defend the other person.
[Use the material in  only if there is evidence the defendant used deadly force. Omit brackets and number.]
 But a person is not permitted to use deadly force unless he reasonably believes the use of deadly force is necessary to protect the other person against (death or serious physical injury) (the commission of a forcible felony).
A person is not required to retreat before resorting to the use of physical force to defend another person if he is (lawfully (entering) (remaining) in a (dwelling) (residence) (vehicle)) (on private property (owned) (leased) by the person) (in a location the person has the right to be).
The state has the burden of proving beyond a reasonable doubt that the defendant did not act in lawful defense of [name of person defended.]. Unless you find beyond a reasonable doubt that the defendant did not act in lawful defense of [name of person defended.], you must find the defendant not guilty (under Count ______).
(As used in this instruction, an “initial aggressor” is one who first (attacks) (or) (threatens to attack) another.)
As used in this instruction, the term “reasonably believe” means a belief based on reasonable grounds, that is, grounds that could lead a reasonable person in the same situation to the same belief. This depends upon how the facts reasonably appeared. It does not depend upon whether the belief turned out to be true or false.
(As used in this instruction, “deadly force” means physical force which is used with the purpose of causing or which a person knows to create a substantial risk of causing death or serious physical injury.)
(As used in this instruction, the term “serious physical injury” means physical injury that creates a substantial risk of death or that causes serious disfigurement or protracted loss or impairment of the function of any part of the body.)
(As used in this instruction, the term [Insert name of forcible felony within quotation marks.] means [Insert definition of the forcible felony. See Notes on Use 5 and 8.].)