A person is privileged to threaten or intentionally use force against another for the purpose of preventing or terminating what the person reasonably believes to be an unlawful interference with his or her person by such other person. The actor may intentionally use only such force or threat thereof as the actor reasonably believes is necessary to prevent or terminate the interference. The actor may not intentionally use force which is intended or likely to cause death or great bodily harm unless the actor reasonably believes that such force is necessary to prevent imminent death or great bodily harm to himself or herself.
The reasonableness of a person's belief under sub. (1) is judged from the position of a person of ordinary intelligence and prudence in the same situation as the defendant, not a person identical to the defendant placed in the same situation as the defendant.
Mitigating circumstances. The following are affirmative defenses to prosecution under this section which mitigate the offense to 2nd-degree intentional homicide under s. 940.05:
(b) Unnecessary defensive force. Death was caused because the actor believed he or she or another was in imminent danger of death or great bodily harm and that the force used was necessary to defend the endangered person, if either belief was unreasonable.
https://docs.legis.wisconsin.gov/statutes/statutes/940/i/01#:~:text=940.01%20First%2Ddegree%20intentional%20homicide,of%20a%20Class%20A%20felony.