Just to share the laws here in Nevada:
In a nutshell, any other place outside of the home (or any temporary place of residence, like a hotel, RV, guest house, etc), one can fire only if the following conditions are met:
1. There is a clear and imminent physical threat that is readily capable of being carried out, that is likely to cause one (or any other person in his or her presence) death or serious bodily injury; Nevada law specifies that a REASONABLE fear (as opposed to a bare fear) sufficient to arouse in an normal person the fear of death or serious bodily injury, is sufficient cause to employ deadly force, given:
2. That the assailant may be fired upon if he/she approaches within 21 feet or less when armed with any weapon other than a firearm, said weapon capable of inflicting a blunt force trauma injury (such as a baseball bat, pipe, chain, wood board or club, etc) and/or capable of penetrating the chest cavity or eye socket (such as a switchblade, knife, ice pick, screwdriver, etc); PROVIDED that #1 above also applies;
3. That the assailant may be fired upon if he/she has met the requirements of #1 above, and is in possession of a firearm at any distance (even outside of the minimum 21-foot distance);
4. That the assailant may be fired upon if he/she has no weapon but has the physical barehanded ability or has displayed the intent to cause death or serious bodily injury, after first satisfying #1 above; It can also be the physical difference in the ability of the shooter to defend himself against the same attack (for instance, a girl can shoot a guy with no weapon if it appears that he can physically overwhelm her and inflict death or serious bodily injury, or in the case of a guy fending off the attack of a group of unarmed attackers).
Nevada law stipulates that in the absence of any CONVINCING evidence to the contrary, and provided the shooter acted within the parameters noted above, that the shooting shall fall under that of justifiable homicide or excusable homicide. The term CONVINCING shall apply to the review of the District Attorney, who has the ability to rule on the case and dismiss the case, or recommend the case to a jury trial. Classically, the DAs here have been very gun-friendly.
In the home, the law is clear: any person who manifestly attempts or endeavors to enter the home of another thru surrepitious means or by violent or tumultuos means, or has entered the home of another by these means, can be fired upon by any person then living or residing or visiting inside that same home, and that in the absence of CONVINCING evidence to the contrary, the shooting shall be ruled justified or excusable, and no criminal or civil charges may be brought against the shooter by any interested party. That means no lawsuits for unlawful death or recovery of damages for personal injury. The law actually states this, and even says "the killing, having appeared justified or excusable, the slayer shall be fully acquitted."
I love my State!
Hope that helps.