When will a judge ask a defendant to plead not guilty to a charge of sexual assault?

"In criminal cases, even in the absence of a request, a trial court must instruct on general principles of law relevant to the issues raised by the evidence and necessary for the jury's understanding of the case." ( People v. Martinez (2010) 47 Cal.4th 911, 953 [105 Cal.Rptr.3d 131, 224 P.3d 877] .) The trial judge has a duty to instruct as to defenses " only if it appears that the defendant is relying on such a defense, or if there is substantial evidence

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supportive of such a defense and the defense is not inconsistent with the defendant's theory of the case. [Citation.]" ( People v. Breverman (1998) 19 Cal.4th 142, 157 [77 Cal.Rptr.2d 870, 960 P.2d 1094] .) " However, when a defendant presents evidence to attempt to negate or rebut the prosecution's proof of an element of the offense, a defendant is not presenting a special defense invoking sua sponte instructional duties. While a court may well have a duty to give a "pinpoint" instruction relating such evidence to the elements of the offense and to the jury's duty to acquit if the evidence produces a reasonable doubt, such "pinpoint" instructions are not required to be given sua sponte and must be given only upon request. [Citations.] " ( People v. Saille (1991) 54 Cal.3d 1103, 1117 [2 Cal.Rptr.2d 364, 820 P.2d 588].)