Exactly! I found this two sentences on an other site with rule "interpretations": Until he has possession of the ball he must give the runner some way to get to the base. Obstruction can NEVER be called on a fielder for blocking a base; when he has possession of the ball.
If the situation starts with a batted ball, then i agree that a fielder is still in the act of fielding if the ball deflects of the fielder and "the ball is within the fielder's immediate reach."