Disclaimer: IANAL, but I dated one who specialized in this, so I got an earful on more than one occasion. This is called the "duty to retreat", and while it is generally true that in most situations you have a duty to retreat if you can and if a reasonable person, placed in your situation, would not feel threatened. There are numerous exceptions, however. For example, since we're making generalizations, it's generally not the case that you have a duty to retreat within your own home, if your attacker does not also live there.

(btw, it's "imminent")