Force runner question - ASA

[wolraht]

Got a question for all you umpiring pros.

Here is the situation. Runners at 1B and 2B. No outs. Lazy fly ball hit to short center field. Balls drops. Runners had not advanced expecting it to be caught. Runner from 2B starts running to 3B. Throw comes in to 3B short of the bag. Third baseman catches the ball and attempts to tag the runner from 2B. The runner stops and dodges backward to avoid the tag.

Umpire calls the runner out for retreating back toward 2B when he was a force out runner to 3B.

Is this the right call? The only rule I have been able to find in the ASA rulebook concerning retreating toward a previous base being an out is a batter-runner retreating toward home plate to avoid a tag.

Can you guys help me out here? I would like to be able to argue this if it is wrong and it happens again.