Base runners cannot leave the base until the batter makes contact with the ball - fair or foul. If the base runner attempts to gain an advantage by leaving the base before batter contact, or on a check swing or miss, that runner will be called out.

A base runner shall NOT be called out when it is obvious the base runner was walking off the base as a result of mistakenly thinking ball 4 had been called. This would not be considered an attempt to gain an advantage.