Sharing what I learn here...

[youngump]

Originally Posted by MD Longhorn

Instead of yelling back at you, I'll let you try to support that by rule. What rule are you using to make the claim that interfering with a fielder trying to field a ball that is currently in foul ground (and, as you say, "has a chance to become fair") is an out.

As I started with above, I came into this discussion believing you were right about this. I still mostly think you are but that the book could be a lot better on this.
That said, let me play devil's advocate for a moment to illustrate the problem I have with the way this is written. If the rule is meant to be interpreted the same way, then why is there a difference between the rules:
8-2-F: When the batter runner interferes with a fielder attempting to field a batted ball
8-7-J-1: When the runner interferes with a fielder attempting to field a FAIR batted ball. [Emphasis added]
(references from 2005 book, hopefully the haven't moved or changed)
[Also see the definition of a foul ball which only references runner]

You could argue that the definition of making a play saves you (it can't be a play if it's an attempt to field a foul ball since that's not an attempt to make an out.) But this has two problems. One you have the slow pitch third strike problem. And two you have the problem that it renders the rule about a ball being foul when the defense is interfered with superfluous (unless you consider the first the solution to the second).