Question: Can you “stand your ground” according to halacha as George Zimmerman allegedly did when he killed Trayvon Martin?
Answer: According to halacha, if someone is running after you to kill you, that person is classified as a rodef and you may kill him. However, this is only the case if you have no other option. If wounding the rodef is sufficient to stop him, you may not kill him. If you do nonetheless, you are a murderer (see Rambam, Hilchot Rotzei’ach 1:6,7)
The Mishnah L’Melech, however, takes a different position (see his comments to the Rambam’s Hilchot Chovail U’Mazik 8:10). He argues that only a bystander has to assess whether killing a rodef is necessary. In other words, if A is trying to kill B in front of bystander C, C may only kill A if he has no other recourse available. If he can save B by wounding A, he may not kill A.
The victim, however – in other words, B – need not assess whether killing A is necessary or not. His life is in danger and he is permitted to kill A without making any calculation as to whether killing him is necessary or whether wounding him would be sufficient.