What is the test for determining whether a jury convicted a defendant of assault based on whether the jury believed he struck his girlfriend with a club?

defendant did not testify at trial and only called his estranged wife to testify as to his character, his guilt turned on whether the jury believed the victim. In closing argument, defendant argued the evidence did not show that he struck his girlfriend with a club. He reasoned that, if he had done so, there would have been blood on the club and his girlfriend would have suffered more severe injuries. On this record, we cannot say the trial court's decision was arbitrary, capricious, or the result of whimsical thinking such that it exceeded the bounds of reason. (People v. Henderson, supra, 187 Cal.App.3d at p. 1268.)