Prof. Colin Miller has this very useful post on the character of a "victim" when a defense of self-defense is raised.
that the trial court erred by preventing him from presenting specific
instance evidence concerning the victim's character for violence. The
appellate court, however, agreed with the trial court, finding that
while Fish could have presented opinion and/or reputation evidence
concerning the victim's character for violence pursuant to Arizona Rule of Evidence 404(a)(2), he could not have presented specific instance testimony unless he had knowledge of those instances prior to the killing.
If Fish had this prior knowledge, he
could present such evidence because he would be using it to prove that
those instances of violence made him reasonably fear the victim,
supporting his self-defense case, not (necessarily) to prove that the
victim had a propensity to act violently and likely acted in conformity
with that propensity at the time of the subject crime.
But without that prior knowledge, Fish could only use that evidence for
propensity/conformity purposes, rendering it inadmissible under Arizona Rule of Evidence 405(a).
Mil. R. Evid. 405 tracks the federal rule.
I would add that should the prosecution offer character opinion testimony of the victim's peacefulness, the witness could be cross-examined on the victims alleged specific instances of violence. The purpose would be to challenge the witness's opinion and not to prove the instances of violence.