(dissenting in part). I respectfully dissent because I cannot agree with the majority that, as the case unfolded, the excluded testimony of the victim’s prior violent conduct was either cumulative or marginal.
After a voir dire hearing during which she heard testimony from the defendant’s proposed witness, the judge, without objection from the Commonwealth, made a pretrial ruling that evidence of the victim’s earlier assault and robbery of the defendant’s proposed witness was admissible on the first aggressor issue. *635See Commonwealth v. Adjutant, 443 Mass. 649, 664 (2005) (specific acts of victim’s prior violent conduct may be admitted to support defendant’s claim of self-defense). When the trial began, the Commonwealth’s opening statement strongly suggested that the victim was not the first aggressor. In response, and relying on the pretrial ruling, defense counsel’s opening promised the jury that a disinterested witness would “come in here on probably Monday, maybe Tuesday, depending upon the pace of things,” to show the jurors that the victim was “capable of unprovoked violence” and hence likely the first aggressor. Far from a fleeting reference, defense counsel made the promise toward the end of his opening as the capstone of his assertions that the jurors would hear evidence warranting an acquittal.1
On the fourth day of trial, however, the judge entered an order stating that “upon reconsideration sua sponte [the] court excludes [the] so-called ‘Adjutant evidence’ because the identity of the first aggressor is not a live issue at trial. There is no evidence the defendant was the first aggressor.”2 As a result, the witness that the defense had promised was barred from testifying.
With the record in that state, the defendant requested an instruction to the effect that the defendant was not the first aggressor and that the testimony he had promised in the opening was irrelevant as a matter of law.3 The judge denied the request, stating, in effect, that there was no evidence one way or the *636other on the first aggressor issue, though there was testimony from the defendant that he had seen the victim “rough up” other people. With the door thus opened, the Commonwealth in summation launched into a blistering attack on the defendant’s claim that he inflicted the fatal wound in response to the victim’s assault, clearly insinuating that the defendant was, indeed, the initial aggressor.
Though, as the majority correctly states, the judge has the discretion to weigh the probative value of so-called Adjutant evidence against its prejudicial effect, Adjutant, supra at 663-664, the record does not reveal that is what ultimately happened here. To be sure, in first deciding to allow testimony by the victim of the assault and robbery, the judge impliedly ruled that the balance between probative value and prejudicial impact tipped in favor of admitting the evidence. But when the judge altered her ruling in the middle of the trial, she did so not on the ground that the evidence was insufficiently probative but on the ground either that the defendant had so clearly won the first aggressor contest that he did not need the evidence and would gain nothing from its admission or on the ground that the Commonwealth had not introduced any evidence suggesting that the defendant was the first aggressor.4
*637From opening through closing, however, an essential component of the Commonwealth’s case was its claim that the victim never engaged in any acts that put the defendant in fear for his safety. The judge barred the only outside evidence the defendant had to bolster his claim that the victim was the first aggressor. That left the defendant with testimony about his own observations, testimony the Commonwealth dispatched by arguing to the jury that it “is only useful to you if you can trust it. And this information by the defendant where, on second thought, . . . he has seen [the victim] eff people up, that’s not worth anything to you because you can’t trust him.”
Adjutant, 443 Mass, at 664, holds that “where the identity of the first aggressor is in dispute and the victim has a history of violence ... the trial judge has the discretion to admit evidence of specific acts of prior violent conduct that the victim is reasonably alleged to have initiated, to support the defendant’s claim of self-defense.” The evidence excluded here, like that proffered in Adjutant, “went directly to the heart of the case’s central dispute —• whether [the victim] was the initial aggressor in his final altercation with [the defendant].” Id. at 666. The posture of the case contrasts starkly with Commonwealth v. Gaynor, relied on by the majority, where the victim conceded his role as the first aggressor. Commonwealth v. Gaynor, 73 Mass. App. Ct. 71, 75 (2008) (excluding Adjutant evidence). That concession eliminated any prejudice from the exclusion of Adjutant evidence because “the identity of the first aggressor was irrelevant to the jury’s consideration of the case as submitted to them by the judge.” Id. at 76. Moreover, the judge in *638Gaynor consistently denied the defendant’s motion for Adjutant evidence, rather than initially allowing it. See id. at 75.
Here, the judge first allowed the evidence, then excluded it after counsel promised to provide it, then declined the defendant’s request for an instruction that he was not the first aggressor and, finally, permitted the Commonwealth to spend its entire summation telling the jury that the victim engaged in no aggression for the defendant to fear. In that context, midtrial exclusion of the evidence created a risk of unfair prejudice that the Commonwealth exploited to full effect.
I would reverse.
Contrast Yeboah-Sefah v. Ficco, 556 F.3d 53, 76, 78 (1st Cir.), cert. denied, 130 S. Ct. 639 (2009) (general promise that “both ‘[psychologists and psychiatrists’ would testify” was not “specific, significant and dramatic promise”); United States vs. Patwardhan, U.S. Dist. Ct., No. ED CR 08-00172 (C.D. Cal. July 18, 2009) (prejudice from opening statement was limited because defense counsel’s reference to evidence was “very brief mention amongst dozens of other subjects,” taking up only eleven lines of twenty-three page transcribed opening, and Adjutant evidence was provisionally admitted subject to foundation that counsel failed to provide), aff’d, U.S. Ct. App., No. 09-50487 (9th Cir. Mar. 18, 2011).
The judge’s reversal was made in response to the Commonwealth’s motion for an Adjutant instruction, which is designed to protect the Commonwealth, not the defendant, see Commonwealth v. Sommer, 77 Mass. App. Ct. 907, 908 (2010), and for limitations on — but not exclusion of — the Adjutant testimony.
The requested instruction stated as follows:
“You recall that in his opening [defense counsel] indicated that he would produce a witness to testify about certain prior conduct of the *636victim .... That testimony would have been admissible if there was a question in the case of who was the first aggressor. It is a trial lawyer’s job to consider all possibilities and therefore, if the question of who was the first aggressor was a live issue I would have allowed [defense counsel] to produce that witness.
“However, based upon the evidence actually submitted I have ruled that there is no question that the victim was the first aggressor. There is no evidence that the defendant was the first aggressor, and [you] must accept as fact that the decedent was the first aggressor.
“Therefore, I have ruled as well that the calling of such a witness is unnecessary.”
The judge explained the basis for her ruling in the course of the following colloquy:
The court: “Well, let me ask you this. Under pre-Adjutant and maybe, [defense counsel], you would be the better one to answer this. Is there any indication in the evidence that you have, or intend to offer, that the defendant knew of the [assault and robbery] incident *637[about which the defendant’s witness would testify] and what it would produce?”
Defense counsel: “He knew of that particular incident? No way.”
The court: “All right. So under pxe-Adjutant that would be the condition precedent.”
Defense counsel: “Correct.”
The court: “And given the condition precedent to Adjutant-type evidence not being present, which is the basis of my ruling, then I find no evidence of the deceased not being the first aggressor, if you will.”