What is the test for a defendant to be convicted of aggravated assault on a peace officer?

The crime of aggravated assault on a peace officer requires that the officer be "engaged in the performance of his . . . duties" at the time of the assault. ( 245, subd. (d)(2).) The officer must be acting lawfully. If the officer used excessive force or detained the defendant without justification, the defendant may be found guilty only of the lesser offense of simple assault. (People v. White (1980) 101 Cal.App.3d 161, 166.) The trial court has a sua sponte duty to instruct on lawfulness if there is sufficient evidence the officer was not lawfully performing his or her duties. (People v. Gonzalez (1990) 51 Cal.3d 1179, 1217 ["disputed facts bearing on the issue of legal cause must be submitted to the jury considering an engaged-in-duty element"], superseded by statute on another point as explained in In re Steele (2004) 32 Cal.4th 682, 690.)