In the trial of criminal cases charging the use of force against another where the issue of defense of self or another, defense of duress or coercion, or accidental harm is asserted, a defendant shall be permitted to introduce either or both of the following in establishing the reasonableness of the defendant's apprehension that death or serious bodily injury was imminent, the reasonableness of the defendant's belief that he had availed himself of all available means to avoid physical combat or the reasonableness of a defendant's perception of the amount of force necessary to deal with the perceived threat:
Nothing in this section shall be interpreted to preclude the introduction of evidence or expert testimony as described in clause (a) or (b) in any civil or criminal action where such evidence or expert testimony is otherwise now admissible.
Mass. Gen. Laws ch. 233, § 23F