This interpretation was posted on 4/30/19:
188.8.131.52 A fielder shall not at any time obstruct a runner rounding a base.
184.108.40.206 A fielder shall not at any time obstruct a runner returning to or leading off a base.
A warning for obstruction on rounding, returning or leading off a base will be issued when the defensive player is not making a play on this runner and is merely in a position that obstructs the runner. If the defensive player is making a play on the runner, she will be charged with obstruction, but not given a warning. Example: The runner at first base leads off and is returning to the base. The first baseman, in an attempt to get her out, obstructs the runner coming into first base. The defensive player is charged with obstruction, the runner is safe at first, but there is no warning for “rounding or returning obstruction” since a play was being made on the runner.