Self-defence Against the Innocent

Do we have the right to defend ourselves against innocent aggressors? If I amattacked in a lift by a knife-wielding lunatic, may I kill or maim him to protect my own life? On one view the insane man’s plight is his bad luck and I am under no obligation to let it be transferred to me. On the opposing view it is my bad luck to be under attack and I have no right to transfer it to an innocent man by killing him to protect myself. It is perhaps becauseneither of these opposing viewpoints is obviously preferable to the other that there is no consensus about the question. Nevertheless we can find considerations for favouring the first view over the second.