Occasionally, new case law will generate an issue where none had been recognized before. It may also happen that an issue is not discovered until after the opening brief has been filed.
If the issue has not been raised and argued in the opening brief, it must be the subject of a supplemental brief. The proper practice is to submit a motion for leave to file a supplemental brief at the same time that the brief is submitted. The motion should briefly outline why the issue was not in the opening brief and its significance to the case. The brief will not be filed without permission of the Presiding Justice. (Cal. Rules of Ct., rule 8.200(a)(4).) If the brief is filed, the court will provide the respondent with an opportunity to file a response. Unless the court’s order has specifically requested the filing of a reply brief by appellant, you must request permission to file one.