New Jersey self defense requires the defendant to have a reasonable belief about three subjects:
The force defendant is using must be immediately necessary – in other words the defendant must believe that the unlawful force will be used against him at the time that he acts;
the force used against the defendant must be unlawful – this defense is not available to the aggressor;
the amount of force which the defendant uses must be necessary – this defense is unavailable if the actor is unreasonable in his belief about the amount of force necessary and if acting on this unreasonable belief the actor uses an excessive amount of force.