SECTION 98 IPC : Private defense against an act committed by a person who lacks capacity for reason, etc. Every person has the same right to a private defense against an act as he would have if the act were an offense, even when an act that would otherwise be a certain offense is not that offense due to the person performing the act’s youth, lack of understanding maturity, insanity, intoxication, or any other mistake on their part.
Illustrations
Z makes an attempt to kill A while insane, but Z is not at fault. The right to private defense is still available to A, just as it would be if Z were sane.
When Z, in good faith, believes that A is a housebreaker and attacks A after A enters a house at night that he is legally allowed to enter, Z violates the law. Z does not violate the law by attacking A in this instance because of a misunderstanding. But A is nonetheless entitled to private defense against Z, just as he would be if Z weren’t acting in error.