I believe that the facts of the incident are not in dispute, because of ample video evidence: Rittenhouse was attacked, tried to escape, and when he couldn't escape, he used his rifle on the attackers. However, he is a minor and was therefore in possession of a firearm potentially illegally. If so, does this fact make it impossible for him to claim self-defense?
Engaging in unlawful conduct does not completely preclude a claim of self-defense under Wisconsin law
...but it does raise the bar in some circumstances:
- Criminal conduct by the defendant removes the presumption that "force was necessary to prevent imminent death or great bodily harm" when defending against unlawful forced entry to one's own property.
- A much higher burden on use of force is imposed if engaging in unlawful conduct that is "of a type likely to provoke others to attack him or her and thereby does provoke an attack."
- Anyone intentionally provoking an attack by any means, lawful or unlawful, "with intent to use such an attack as an excuse to cause death or great bodily harm to his or her assailant," is not entitled to self-defense at all.
Section 939.48 of Wisconsin law governs the standards for self-defense.
939.48(1) sets out the general standard:
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.
939.48(1m)(ar) provides presumptions in favor of the defendant and no duty to retreat when defending against unlawful entry to one's own property (an implementation of the castle doctrine), but those presumptions are removed by 939.48(1m)(b)1. if (among other things), "[t]he actor was engaged in a criminal activity."
More relevant to a case that occurred outside is 939.48(2), which lays out how provocation affects a claim of self-defense:
(a) A person who engages in unlawful conduct of a type likely to provoke others to attack him or her and thereby does provoke an attack is not entitled to claim the privilege of self-defense against such attack, except when the attack which ensues is of a type causing the person engaging in the unlawful conduct to reasonably believe that he or she is in imminent danger of death or great bodily harm. In such a case, the person engaging in the unlawful conduct is privileged to act in self-defense, but the person is not privileged to resort to the use of force intended or likely to cause death to the person's assailant unless the person reasonably believes he or she has exhausted every other reasonable means to escape from or otherwise avoid death or great bodily harm at the hands of his or her assailant.
(b) The privilege lost by provocation may be regained if the actor in good faith withdraws from the fight and gives adequate notice thereof to his or her assailant.
(c) A person who provokes an attack, whether by lawful or unlawful conduct, with intent to use such an attack as an excuse to cause death or great bodily harm to his or her assailant is not entitled to claim the privilege of self-defense.
To just reply to your question, not the particular case: Committing a crime can hurt your defense, but doesn't always make it impossible. It all depends on which crime you have committed. If you shoot a gun at me but miss me, and I shoot back (in justified self defense) and injure you, then you can't kill me and successfully claim self defence. Even if you are in reasonable fear of your life. Because the whole situation was created by your crime.
On the other hand, if you steal a bar of chocolate in a shop, the shop owner goes mad and tries shooting you, injures you, and looks like he is going to shoot again, then it would be very likely that you can successfully claim self defence if you shoot them first. Stealing a bar of chocolate is a crime, but not one that a shop owner can use as a valid excuse to kill you.
On the third hand, if you were caught raping a woman, that would be a crime that would likely cause a strong reaction, and it would be reasonable to expect you getting beaten up by people finding out (not that it would be right, but you'd have to expect it). In this situation, you can only claim self defense if you are in reasonable fear of your life or of "great bodily harm". The fear must be reasonable - even rapists are usually not killed by a mob. And "great bodily harm" is a legal term for the worst kind of bodily harm, getting beaten up would not be "great bodily harm". So for a succesful claim of self defense, more would have to happen.