There are laws allowing person to shoot intruder in their house. And I can't serve nulls from my own web server? That would be ridiculous.
A farmer here in UK stirred up a whole load of shit when he shot two burglars [1] trying to escape from his property.
Some places in the USA have "stand your ground" laws. These say you aren't required to retreat, that you can "stand your ground", that you can use (legally) leathal force without requiring that your back is against the wall.
As for people running away, the only way I see self defence working is when they still pose an 'imminent threat to life' which seems rather hard to argue.
I've read but couldn't find again the story of someone shooting a tief to get back his VHS player and walk free.
I'm not arguing for actually using the law to shoot people: I don't ever want to be in that situation myself, but I'm saying depending on the situation you do in fact have the law on your side.
That isn't normal, though. It's likely that you were already feuding, and so the law will look askance at you for not bringing authorities into it much earlier.
I think all of those cases are covered by any imminent threat clause, and thus do not need special exemptions. Just like there isn't an exemption that you are not allowed to shoot a retreating person. It simply follows because (with exceptions) retreating people aren't imminent threats.
Florida [1], for example, says:
> ... A person who uses or threatens to use deadly force in accordance with this subsection does not have a duty to retreat and has the right to stand his or her ground if the person using or threatening to use the deadly force is not engaged in a criminal activity and is in a place where he or she has a right to be.
In section 0776.013, the castle doctrine is also noted, but is more expansive, and includes the use of deadly force even if there is no threat of imminent harm.
[1] http://www.leg.state.fl.us/statutes/index.cfm?App_mode=Displ...
The US tends to be a little more prescriptive, leaving a situation where different jurisdictions have more specific requirements for defining what constitutes self-defense.
Juries in the UK tend to have significantly more responsibility for making judgments like these, leading to a system where evolving views of what is right and wrong can result in standards naturally evolving over time, rather than being fixed by what people thought was okay thirty years ago.