When can you use deadly force?
Scenario # 1
You answer the door and are confronted by a neighbor you really don't know but have seen at house a few doors down. There is conversation between the two of you but nothing specific. (Like; Hi my name is blah blah and I live a few doors down wonder if I could speak with you ?)   He suddenly burst into your home. Would you use deadly force?
This is all you know.
Scenario # 2
Your in the yard doing work when you turn around, there is a person running toward you. You have never seen this person and he does not speak as he is closing in on you. You Pull your weapon but he is too close to avoid. Would you use deadly force?
This is all you Know.

No and no, but I would draw in both circumstances.

Usually the concept to look out for is DISPARITY of force. Is the guy a 95-pound weakling attacking a 250-pound college quarterback? In that case, deadly force would not be justified. However, if the stats were reversed, it'd likely be allowable to kill the attacker.

Even in states like New Mexico, where 'violent and tumultuous entry' is grounds for deadly force, and we have no duty to retreat, the concept of disparity of force is paramount.

The question a jury will ask is: How much of a threat is the other guy to you?

Too bad, really; I personally believe that a man's home is his castle, and NO ONE, for ANY reason, should disturb him there.

Scenario 1 = Repel Boarders..................
Scenario 2 = Someone flopping around on my lawn like a carp out of water...........

Both scenarios result in a call to the police, and EMS.

Frank that is a point I was never aware. I was hoping when I started this thread I would get these sort of answers so we could all be better informed. Thanks

Quoted: Usually the concept to look out for is DISPARITY of force. Is the guy a 95-pound weakling attacking a 250-pound college quarterback? In that case, deadly force would not be justified. However, if the stats were reversed, it'd likely be allowable to kill the attacker. Even in states like New Mexico, where 'violent and tumultuous entry' is grounds for deadly force, and we have no duty to retreat, the concept of disparity of force is paramount. The question a jury will ask is: How much of a threat is the other guy to you? Too bad, really; I personally believe that a man's home is his castle, and NO ONE, for ANY reason, should disturb him there.

I am not familiar with any cases which suggests disparity of force has any impact when a man is in his castle.  It does on the street when the attacker(s) do not have similar weapons.  Neither scenario from OP suggests the ability to retreat.  In Virginia at least, I believe shooting in either circumstance may be justified.  

#1 probably draw and challenge.
#2 if he is closing that quickly, then the sequence becomes: sidestep, pivot and push, then draw. His next action would determine whether or not I shot.

If someone is closing quickly, you can change your direction a lot easier than they can, and you have the advantage of being able to choose when and how to move. Then their reaction time works in your favor. (and yes, you can game this scenario where this might not work, but I'm going from how I read it.)

Forget trying to draw until you create separation. Separation = time.

In California, there are two legal concepts that pply to your scenarios.

1.  Castle Doctrine - if someone breaks into your home, the one who breaks in is presumed to have intent to do great harm to you and/or your loved ones.  You are allowed to use deadly force to defend yourself and your loved ones inside your home.

2.  AOJ (ability, opportunity, jeopardy) - If someone is threatening to kill or do great bodily harm to you or your loved ones you may use deadly force to defend them, whether you are in your home or not.  After the fact, the AOJ principle will be applied to determine if the deadly force was justified.

2a)  Ability - did the assailant have the ability to kill or do great bodily harm?  

A simple version of this concept is, did they have a weapon?  Let's say you saw they had only knife.

2b)  Opportunity - did the assailant have the opportunity to do great bodily harm?  

A simple version of this concept is, did they have direct access or were they kept away by a chain link fence.  If there was a chain link fence, and they made no attempt to circumvent the fence, then they had no opportunity to use the knife you saw they had.  If there was no fence, then they had opportunity.

2c)  Jeopardy - did you feel your life or that of your loved ones was threatened?

Basically, were you afraid for your life?  Let's see now, so far we have an assailant who has a knife and is a short from you running at you perhaps yelling, "I'm gonna kill you, you MF!"  This might reasonably cause one to be in fear of his life.  

Draw and shoot to stop the threat.  <-- even here in California.

I would like to have the option of shooting both but don't see how it would be legal. I would certainly draw.

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Quoted: When can you use deadly force? Scenario # 1 You answer the door and are confronted by a neighbor you really don't know but have seen at house a few doors down. There is conversation between the two of you but nothing specific. (Like; Hi my name is blah blah and I live a few doors down wonder if I could speak with you ?)   He suddenly burst into your home. Would you use deadly force? This is all you know. Scenario # 2 Your in the yard doing work when you turn around, there is a person running toward you. You have never seen this person and he does not speak as he is closing in on you. You Pull your weapon but he is too close to avoid. Would you use deadly force? This is all you Know.

Scenario #1 you have some conversation with a person you know to be a neighbor he says ... wonder if I could speak to you?  He suddenly burst into your home.  My take on that is there is something he is concerned or upset about or something going on - so at that point I do not see an imminent threat. I recognise that the situation could deteriorate. I would be more inclined to say Hold it Right There Thats Far Enough and while I might place my hand on my pistol with my gun side away from him I would probably not draw it until something indicated a threat.

Scenario # 2 I believe is highly unlikely at least where I live,  but unless he had a weapon the question becomes is he a threat and if so to what degree.  The safest rule to use regarding deadly force is in defense of life.  If  you pull your weapon and he is stupid enough to physically assault you it may be a case of him commiting suicide by him pulling on the gun while you just hold onto it.
Probably the best answer to #2 is the same thing I told my Sgt. 20 yrs ago when he asked me what are you going to do if you are checking a building with a revolver in each hand and a burglar jumps out at you.  I told  him I'm going to do that same thing that you are going to do with one revolver in your hand I'm going to hit him with it.  Note: guns were tougher back then - they were made out of steel.

I think both these guys deserve a left cross but if you can avoid shooting them do so.

The info in this thread just keeps getting better and each one provides a different outlook on these senarios.
Senario #3
You pull into the local Wallyworld parking lot and you and your 10 yr old daughter get out. Just as your door slams locked a stranger pops up from the front of the car parked on your daughters side.(Hopfully She knows to boogie around the back of the car to your side.) She does. The man is unkept and headed in your direction all the while asking for a couple bucks. You of course are armed with your blade. You in a loud voice tell the man to stay back. He continues to come forward.

gopeterson  What would be similar weapons??? bare kuncs, to bare knucs. I would think any weapon used in the hands of an intent man or woman would or could be deadly. Asking because I would like to see this from a different point of view.

For # 3, at this point I begin yelling very loudly for the man to stop. Depending on the exact situation, I yell help police, while assuming a defensive stance.

One hand moves to where my spyderco is located. I can draw, open, and assume a fighting stance pretty quickly (point down, cutting edge out)

I continue to create noise and draw attention. Depending on how the guy moves, I may do a take down, or I may go for removing the threat using my blade. I may even simply run away to the store.

It all depends on whether or not I can safely remove myself from the situation, or how much of a threat the guy continues to be...

In AL,

The "Castle Doctrine" bill removes the "duty to retreat" if an individual is attacked in his or her home, vehicle, place of business, or any other place he or she has a legal right to be. This legislation also states that victims may use necessary force to defend themselves against the attacker.

What you need to know is that use of deadly force is appropriate when a person is "in imminent fear of serious bodily injury or death."

This is judged by a subjective, not an objective, test, i.e., it is the perception of the person who used force, not the after-the-fact judgment of a court or jury, that counts. It doesn't matter if you'd known the neighbor since you were a child or had just met him, only whether the jury believes that you, at that moment and in that unique situation, reasonably believed that you were about to be seriously injured or killed by the person against whom you acted.

A couple of notes:

"Disparity of force" applies in a lot of situations, such as where a person responds to verbal threats with a baseball bat. But if you are at rest in your home and are suddenly assaulted by a person, you might reasonably be in fear for your life and respond with deadly force. Or, you might be frail or elderly, and your only recourse to physical force might be with deadly force. In a nutshell, if you are truly in fear for your life, it doesn't matter what kind of force you face, as long as you perceive an immediate, deadly force.

Second, note that the use of deadly force is never justified in defense of property, human life always taking precedence to any physical property of any value. However, if you confront someone destroying/stealing your property and they attack you...

Finally, the disclaimer: the above does not take into account the many state and local laws in effect, and you should check them before acting on the above.

Very well put. I think that most situations where deadly force is used or could be used, there is fear of using it. That fear stems from the question of how do I show a court and jury what made me feel I was in fear of my life. I know I would rather have to explain myself to a court as to why and how I was feeling rather than not be able to. I also think most people no matter how well trained they are retain this cloud of fear when confronted. WELL Trained only means to me that you can process these thoughts faster than with less or no training.  

Quoted: I think that most situations where deadly force is used or could be used, there is fear of using it. That fear stems from the question of how do I show a court and jury what made me feel I was in fear of my life.

Sounds like you have not been threatened seriously enough yet.

You are pretty unlikely to have time to consider very much at all.