2009 Massachusetts Code
PART III COURTS, JUDICIAL OFFICERS AND PROCEEDINGS IN CIVIL CASES
TITLE II ACTIONS AND PROCEEDINGS THEREIN
CHAPTER 233 WITNESSES AND EVIDENCE
Section 23F Admissibility of past physical, sexual or psychological abuse of defendant

Section 23F. 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:

(a) evidence that the defendant is or has been the victim of acts of physical, sexual or psychological harm or abuse;

(b) evidence by expert testimony regarding the common pattern in abusive relationships; the nature and effects of physical, sexual or psychological abuse and typical responses thereto, including how those effects relate to the perception of the imminent nature of the threat of death or serious bodily harm; the relevant facts and circumstances which form the basis for such opinion; and evidence whether the defendant displayed characteristics common to victims of abuse.

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.