force outs

Question
Hello,
I was wondering if a runner on first has to leave the base if the hitter hits a grounder to first. We play in an adult softball league and there was a runner on first. The batter hit a grounder to the first baseman and he tagged first base to get the batter out. Does the runner on first still have to advance or are they no longer in a force out situation?

Answer
this would no longer be a force on R1 as the b-r was put out.  R1 is once again legally entitled to occupy the base as there is now no b-r "forcing" him from the base.

Had R1 been tagged 1st (even while standing on 1st) and then the base stepped on you would have a double play.

Mark