Greenmonsters
Wannabe Duck Boat Owner
If a defender was stationed just to the front and inside (on home plate side of and just toward 2nd base side of 3rd) they are giving the entire base to the runner and they have any path they want to the bag. Even if a runner for some reason chose a path to the home plate side of the base, it is available to them. I dont see how any umpire could judge this positioning to be obstruction.
I think MTR's subsequent post addresses this situation appropriately.