People v. Breverman - 19 Cal. 4th 142, 77 Cal. Rptr. 2d 870, 960 P.2d 1094 (1998)

Rule:

In a noncapital case, error in failing sua sponte to instruct, or to instruct fully, on all lesser included offenses and theories thereof which are supported by the evidence must be reviewed for prejudice exclusively under Watson. A conviction of the charged offense may be reversed in consequence of this form of error only if, after an examination of the entire cause, including the evidence, Cal. Const. art. VI, § 13, it appears reasonably probable the defendant would have obtained a more favorable outcome had the error not occurred.

Facts:

Defendant shot and killed a man who was among a group of men destroying defendant's car, claiming fear for his safety. Defendant was charged with murder, justifiable homicide, and the lesser necessarily included offenses of voluntary and involuntary manslaughter. The voluntary manslaughter instructions were premised entirely on the theory of unreasonable self-defense. Defendant was convicted of murder and challenged his conviction, claiming that the trial court erred by failing to instruct, sua sponte, on a heat of passion theory of voluntary manslaughter, Cal. Penal Code § 192(a), which was also supported by the evidence. The appellate court agreed with defendant, reversed his conviction, and remanded for a new trial. The State appealed. 

Issue:

1. Was the trial court required, sua sponte to instruct fully on all lesser necessarily included offenses supported by the evidence? 
2. Did an erroneous failure to instruct necessitate an automatic reversal of conviction? 

Answer:

1) Yes. 2) No.

Conclusion:

The Court held that defendant was entitled to a jury instruction on every theory that was rationally supported by the evidence but that an automatic reversal was not required. Instead, a determination should be made as to whether the entire cause, including the evidence disclosing the error, produced a miscarriage of justice; accordingly, the court remanded the case to the appellate court for review under the court's standard for reversal.