Who is out in this case ?

It depends on if the Fielder tags the runner or steps on the base first. If the fielder tags the runner first and then steps on the base before the batter gets there we have a double play and they are both out. If the fielder tags the base first the batter is out but the runner is then considered safe because there is no longer a force play that makes the runner leave the base.

I saying this as a player who has had this play called this way a couple of times exactly the way I have described, however, going by some of our umps knowledge of the rules I may be wrong. If I am I am sure someone else will let me know.