Self-defence, when is it lawful to hit someone back?

Section 48 of the Crimes Act 1961 provides that everyone is justified in using reasonable force to defend themselves or another person. The court asks whether you honestly believed force was necessary, judged on the circumstances as you believed them to be, and then whether the force you used was reasonable in those circumstances. Because a person facing a sudden threat does not need to weigh things carefully, courts recognise that mistakes are understandable, but force that is clearly excessive or continues after the threat has ended can result in a conviction. Preserve evidence such as CCTV, witness details and any injuries you suffered. Do not give a formal statement without legal advice, because the way you describe your state of mind is critical.