HARRISBURG, Pa. — A panel of appellate judges pressed lawyers for Bill Cosby on Monday to explain why the entertainer should have his conviction for sexual assault overturned at the first hearing prompted by Mr. Cosby’s appeal.

Mr. Cosby is serving a three to 10-year sentence for drugging and sexually assaulting Andrea Constand at his home outside Philadelphia after giving her some pills.

His lawyers told a three-judge panel of the Pennsylvania Superior Court that the trial judge should never have allowed the testimony of five other women who said they too had been drugged and sexually assaulted by Mr. Cosby.

The prosecution contended the women’s testimony showed a series of “prior bad acts” that fit the pattern of conduct in the Constand case. But the defense challenged the existence of such a pattern and said the admission of the women’s testimony had hurt the presumption of innocence toward their client.