Q. Can I use a practice or X-Out golf ball?
A. If the Committee hasn’t required that you play a ball that is on the List of Conforming Golf Balls, then you may use a practice or X-Out golf ball. When using an X-Out ball in this circumstance, if there is strong evidence to suggest that the ball does not conform, it must not be used. However, if the Committee says that the ball you play must be on the List of Conforming Golf Balls, then you can use a practice ball but must not use an X-Out ball (see Interpretation 4.2a(1)/2).