Raising a new theory in a reply brief is improper and unfair to defendants. We may decline to consider an argument raised for the first time in a reply brief if no good reason is demonstrated for the delay in raising the point. (Proctor v. Vishay Intertechnology, Inc. (2013) 213 Cal.App.4th 1258, 1273–1274.)
See also this unpub'd opinion today at fn. 7 for the same point.