What is the standard of proof in a sexual assault case?

"As a general proposition a defendant is entitled to an instruction as to any recognized defense for which there exists evidence sufficient for a reasonable jury to find in his favor." (Mathews v. United States (1988) 485 U.S. 58, 63.) Further, under appropriate circumstances, "a trial court may be required to give a requested jury instruction that pinpoints a defense theory of the case by, among other things, relating the reasonable doubt standard of proof to particular elements of the crime charged. [Citations.] But a trial court need not give a pinpoint instruction if it is argumentative [citation], merely duplicates other instructions [citation], or is not supported by substantial evidence [citation]." (People v. Bolden (2002) 29 Cal.4th 515, 558.)