Massachusetts General Laws Part III. Courts, Judicial Officers and Proceedings in Civil Cases (Ch. 211-262) Ch. 233, § 23F

(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.