The laws of self-defence differ in many countries but the general principle is mostly the same. The US allows its citizens to carry a few weapons with them in order to protect themselves; however, they must have a license to carry those arms. On the other hand, Australia is against the use of weapons in self-defence situations and is highly dependent on the police for the protection of its citizens.
Self-defence is an act performed by an individual to protect themselves in case of murderous intent, assault and battery, rape or any other violent act being committed towards them. A plea for self-defence can include any criminal charges or liabilities for committing a crime, causing injury to or death of another person in the situation. You may need to consult a criminal lawyer in order to get specific legal advice.