If the defense of self defense is supported by the evidence but is inconsistent with defendants theory of the case, a trial court is not required to instruct on self-defense sua sponte but must do so only if the defendant requests it. Defendant shot and killed the victim. During trial on an attempted murder charge, prior to defendants testimony, the defense was one of self-defense, but when appellant testified, he said he fired the gun accidentally. In California, self-defense and accidental homicide are mutually exclusive but a defendants assertion of accident may be disregarded by the jury in an appropriate case and instruction on self-defense is not foreclosed when substantial evidence exists that the shooting was intentional and, otherwise, meets the requirements of self-defense. Here, the trial court erred in denying appellants request for instruction on self-defense as substantial evidence supported such an instruction, despite defendants assertion that the gun accidentally fired. The error was prejudicial, requiring reversal of the attempted second degree murder conviction, because the evidence was evenly balanced.