Anthony Brian Walker v. United States

In a criminal prosecution, when an affirmative defense—such as imperfect self-defense—is supported by substantial evidence, does the trial court have an obligation to instruct the jury on that defense sua sponte, even if defense counsel does not request the instruction?

Did the court of appeals improperly fail to follow its own precedent in holding that a proffered jury instruction fails to preserve the defense of imperfect self-defense unless it includes “essential” language providing that the defendant “subjectively believed that the use of deadly force was necessary to prevent death or great bodily harm to himself or others, even though his belief was not objectively reasonable”?