[IronHorse2130]

Sorry if this is too far off topic but I'm sure the answer can be found here.

I was playing softball today and the following happened:

Bases loaded, 1 out. The batter hits a hard grounder to 3rd Base. The 3rd baseman fields the ball and steps on 3rd base. He then tags the runner that was/is standing on 3rd. The runner never left the bag, before or after the ball was hit. It was ruled a double play.

Does the runner on 3rd have to vacate the base or can he stay on the bag? I imagine he can stay on the base but the fielder could have tagged him (even with him standing on the base) and then stepped on the base for the double play. Because he stepped on the base first, that allows the runner on 3rd to do as he wishes, removing the force, correct?