Obstruction

[CecilOne]

Originally Posted by Tru_in_Blu

But in this case, the fielder did not miss a ball at all. She was in the process of making a play which is an attempt by a defensive player to retire an offensive player.

How long is the defender permitted to hold her position while or after making said play? You must answer this if your argument is she "can't go poof".

Come on, missing the ball was not the point; just an example of a fielder impeding without time to evade.

The is based on base runner momentum until the play ends or it passes beyond the runner.
Applying that "can't go poof" concept to the OP etc., means either the runner passes the fielder or the play is beyond them. Excluding deliberate OBS of course.