What is the legal test for a motion for a new trial in a sexual assault case?

"The authority of a trial court in this state to grant a new trial is established and circumscribed by statute. [Citation.] Section 657 sets out seven grounds for such a motion: (1) 'Irregularity in the proceedings'; (2) 'Misconduct of the jury'; (3) 'Accident or surprise'; (4) 'Newly discovered evidence'; (5) 'Excessive or inadequate damages'; (6) 'Insufficiency of the evidence' [or the verdict is against law]; and (7) 'Error in law.' [] . . . Section 657 . . . provides: 'When a new trial is granted, on all or part of the issues, the court shall specify the ground or grounds upon which it is granted and the court's reason or reasons for granting the new trial upon each ground stated.'" (Oakland Raiders v. National Football League (2007) 41 Cal.4th 624, 633-634.)