Criminal Code Act 1899

When a person is unlawfully assaulted, and has not provoked the assault, it is lawful for the person to use such force to the assailant as is reasonably necessary to make effectual defence against the assault, if the force used is not intended, and is not such as is likely, to cause death or grievous bodily harm.

If the nature of the assault is such as to cause reasonable apprehension of death or grievous bodily harm, and the person using force by way of defence believes, on reasonable grounds, that the person can not otherwise preserve the person defended from death or grievous bodily harm, it is lawful for the person to use any such force to the assailant as is necessary for defence, even though such force may cause death or grievous bodily harm.