What is the legal test for a trial court to instruct on defense in a lesser offense?

The rule regarding sua sponte obligation to instruct on defenses is different than the rule regarding lesser offenses. As noted in People v. Sedeno (1974) 10 Cal.3d 703, 112 Cal.Rptr. 1, 518 P.2d 913, ⁴ the trial court is required to instruct on lesser offenses even if it is inconsistent with the defense elected by the defendant if there is evidence from which the jury could conclude that the lesser offense had been committed. (Id., at p. 717, fn. 7, 112 Cal.Rptr. 1, 518 P.2d 913.) However, the trial court is not required to instruct sua sponte on defenses which are inconsistent with the defense theory of the case.

"[T]he duty to give instructions, sua sponte, on particular defenses and their relevance to the charged offense arises only if it appears that the defendant is relying on such a defense, or if there is substantial evidence supportive of such a defense and the defense is not inconsistent with the defendant's theory of the case. Indeed, this limitation on the duty of the trial court is necessary not only because it would be unduly burdensome to require more of trial judges, but also because of the potential prejudice to defendants if instructions were given on defenses inconsistent with the theory relied upon. 'Appellate insistence upon sua sponte instructions which are inconsistent with defense trial theory or not clearly demanded by the evidence would hamper defense attorneys and put trial judges under pressure to glean legal theories and winnow the evidence for remotely tenable and [13 Cal.App.4th 220] sophistical instructions.' " (People v. Sedeno, supra, 10 Cal.3d 703, 716-717, 112 Cal.Rptr. 1, 518 P.2d 913.)