A substantial minority of American states allows people to use lethal force in self-defense (against a reasonably perceived threat of death, serious injury, rape, or some other serious crimes) only when the person can't avoid the danger by safely retreating. This requirement — which is sometimes called a "duty to retreat," but is really a limitation of the right to self-defense — generally doesn't apply when the defender is in his own home, and doesn't apply when retreat would be unsafe: For instance, a defender doesn't have to turn his back on an assailant with a gun in order to retreat.
But the theory is that when a safe retreat is possible, the use of lethal force is no longer necessary to avoid the threat, and therefore no longer justifiable. Better that the defender feel obligated to retreat than that even a guilty attacker get killed. Better that the defendant retreat than that there be a shootout which needlessly injures or kills bystanders, or leads to vendettas. And better that the "defender" retreat than kill someone in ostensible self-defense, but an ostensible self-defense that could be used as a cover for outright murder, for instance if the supposed defender really wasn't in danger, but made up the self-defense story (especially likely when the other witnesses to the confrontation are either the "defender"'s buddies or are dead).
The majority of American states disagrees, probably based on a combination of factors: that limiting self-defense this way interferes with defenders' liberty by denying them the right to stay where they have the right to be and at the same time defend themselves against illegal attack; that limiting self-defense this way interferes with defenders' dignity by forcing them to run away from danger; and that in practice it's so hard to determine when retreat is really safe that it's better not to second-guess defenders' judgment to stand their ground. In those states, lethal self-defense may be used against a reasonably perceived threat of death, serious bodily injury, rape, and some other serious crimes even when the defendant had the opportunity to safely retreat. My understanding is that some states have recently shifted to the no-duty-to-retreat camp.
But it turns out that in a few states, it's illegal to use even nonlethal self-defense if you can safely retreat. The treatises report that this is a very small minority view; even the Model Penal Code, which firmly endorses not just a duty to retreat but also a duty to give in to certain threats as a limit on lethal self-defense, rejects a duty to retreat before using nonlethal self-defense. Still, it appears that Iowa and possibly Minnesota (plus perhaps a few other states) take this view.
This means that if someone threatens you in a public place — even with just a fistfight — you are not entitled to defend yourself, again even only with your fists, if you are able to retreat safely. Your legal right to stay where you want to stay can thus practically be constrained by any bully who threatens you with a fight, even if you think you could physically defend yourself. Someone doesn't like your being with a date of a different race (or of the same sex) and threatens to beat you up if you don't leave a bar (or a street corner)? You have to leave, or if you stay and he starts beating you you would be guilty of assault if you defend yourself. Someone is just a bully who wants to have the fun of making you do what he asks (which is to get away from him)? Same situation.
A case in point, from an Iowa court [UPDATE: link fixed]: Michael Mette, an off-duty Chicago police officer, was sentenced to 5 years in prison in Iowa for punching Jake Gothard in the face, which led Gothard to fall, hit his head, and be seriously (though apparently not permanently) injured.
Gothard had a blood alcohol level of .270 when he got to the hospital. The judge agreed that Gothard and a friend of his were going after Mette and five of his friends, outside of Mette's house. The judge agreed that "It was reasonable under the circumstances to believe that harm might come to [Mette or his friends]." Mette and his friends were not the aggressors. (They may have behaved badly in one respect, which is by taking Gothard's cell phone out of his hand and leaving it in Jake's mailbox, but the judge didn't seem to conclude that this was what made Mette's later actions unjustified.) The evidence the judge related seemed to say, without contradiction, that Mette had hit Gothard only once, and that Gothard had just "pushed [Mette] at least two times, maybe three."
Yet the judge convicted Mette (who had opted for a trial without a jury) simply because "the defendant failed ... to retreat ... or walk away and call the police about the disturbance. Because of his failure to take these steps, the court cannot find that the self-defense justification is available to permit the striking of [Gothard]."
That seems to me wrong: Mette should not have been under a legal obligation to either (1) leave the street where he had every right to be, or (2) surrender the right to self-defense if he didn't leave the street. Perhaps the result should be different when one is using lethal force, though I'm not sure; and I realize that even seemingly nonlethal punches can end up being lethal (or can end up escalating a fight into something more lethal). But on balance, it seems right that the duty to retreat has been almost everywhere rejected as to nonlethal force: It in effects allows bullies far too much legal authority to constrain people's freedom.
Still, State v. Washington, 160 N.W.2d 337 (Iowa 1968), which seems to still represent Iowa law, does indeed put Mette in precisely that position. See also State v. Baker, 160 N.W.2d 240 (Minn. 1968). Mette is apparently appealing; let's hope Iowa courts will revise or limit the duty to retreat on appeal.
Thanks to Sean O'Brien for the pointer; thanks also to this Chicago Tribune opinion column by John Kass for providing an account of the situation, though I recommend that people who are interested in the facts of the case read the judge's opinion.
UPDATE: Thanks to commenter ak47pundit for pointing me to a recent Michigan law that generally abolished the duty to retreat, including the duty to retreat before using nonlethal force; I had originally mentioned Michigan as a state in which such a duty might exist, but have since removed that reference.