R3 "interferes" with F5 on line drive

[Rich Ives]

Originally Posted by David Emerling

Actually, runners (on 3rd) are taught to take their leadoff in foul territory (so as not to get hit by a fair batted ball, like you said) but to return in FAIR territory (after the pitch) so as to block any attempt on the part of the catcher to pick him off - forcing the catcher to throw around him or, better yet, the thrown ball hits the runner and is deflected away allowing him to score. "Lead off in foul, return in fair" is the proper way.
This is proper technique: https://www.youtube.com/watch?v=YaE-725FNCU

In any case, none of this is the point of the question. An answer to a rules question is never, "That would never happen" or "The player shouldn't do it that way." There should always be an answer; because weird things do happen and players sometimes don't do things the way they should.

Maybe return fair if possible on a pick attempt because you can see it coming. It isn't always.

A batted ball is not the same. It's a surprise and it gets there much faster.

You lead off as far from the base as F5.

The closer to HP the more foul you get.