[Az.Ump]

RULE 7.08
Any runner is out when -

(5) [Softball only] the runner fails to keep contact with the base to which that runner is entitled until the ball has been batted or reaches the batter or in Junior/Senior/Big League, the runner fails to keep contact with the base to which that runner is entitled until the ball has been released by the pitcher. When a runner is off a base after a pitch or as a result of a batter completing a turn at bat, and while the pitcher has the ball within the eight (8) foot radius circle, the runner must immediately attempt to advance to the next base or return to the base the runner is entitled. NOTE: If the pitcher has possession of the ball within the pitcher's circle, and is not making a play (a fake throw is considered a play), runners not in contact with their bases must immediately attempt to advance or return to base.
PENALTY: The ball is dead. "No Pitch" is declared, and the runner is out. Eight (8) foot radius circle must be properly marked.

Fair Ball, January 2002
Situation 28: On a base on balls, the pitched ball is immediately returned to the pitcher in the eight-foot circle. The batter runs to first base, rounding the base in a move toward second base. While ten feet off the base, the runner stops and returns immediately to first base. The umpire calls the runner out. Correct or incorrect?
Ruling: Incorrect. The rules was not designed to allow the defense to get easy outs, although we, as umpires, sometimes try to use it that way. The defense has the responsibility to get the runner stopped at first base or to try and throw the runner out at first or second base. As long as the runner immediately attempts to advance or retreat after the stop, the runner has done nothing wrong.

It's all I could find.

Paul