According to the NCAA Men’s Basketball Rules Book, if a defender hits or makes illegal contact with the offensive player’s arm holding the ball, it is considered a foul under Rule 10 - Fouls and Penalties. Specifically:
IAW Rule 10, Section 6, Article 1 defines a personal foul as any illegal physical contact with the ball handler, including hitting the arm while holding the ball.
The rule states that a personal foul occurs when a defender makes illegal contact with the arms, hands, or body of the offensive player in a way that affects their ability to control the ball, shoot, or pass.