What is the test for establishing self defence in a personal injury case?

In order to establish self defence, a defendant does not have to show that the claimant struck the first blow or was actually going to hit him: Slauenwhite v. Walker, [2000] N.S.J. No. 268 (N.S.S.C.). At para. 16, Hall J. stated: …the right to repel force with force is not confined to warding off a blow. Tort law does not stay the hand until a battery has actually be [been] committed, for if it did it might "come too late afterwards" to do any good. A person may, therefore, strike the first blow and still claim the privilege of self-defence, as long as the purpose of the blow is to halt future or further aggression and not to punish the attacker for his past aggression. In short, "self-defence means defence, not counter-attack." The privilege of self-defence is available not only where harm is actually threatened by an attacker, but it may also be relied upon by a person who reasonably believes that he is about to be attacked. Even though he is mistaken as to whether he is in danger he will be excused as long as he has been reasonable in his error.