Quoting Evans from 7.09(a):
A batter has an inherent obligation to avoid the catcher fielding the ball just as a runner must avoid an infielder in the act of fielding [a batted ball].
I like the phrase "inherent obligation" and feel it can apply to several basics of baseball. I also feels it applies to a fielder's need to avoid a runner unless the fielder is in possession of the ball or is required to enter the runner's path to glove the ball. Too many have come to excuse "blocking" a base merely because a fielder can reach away to touch a ball when, in fact, there is no need for him to "block" the runner's path before receiving the throw.
Both OBR and J/R in their discussions of being in "the act of fielding" add further detail to support the concept that it is the "inherent obligation" of a fielder to avoid a runner excepting the need to tag or field the ball. NCAA with their recent rule change showed they had to eliminate the words "act of fielding" from their definition of obstruction so as to impress this fact upon umpires.
Just my opinion,
Freix