Foul ball, or not?

[lawump]

To the original poster:

I think, to summarize, in order to answer your question: We need to know where the ball was when it was touched by the (offensive or defensive) player.

Since the ball did not come to a stop (and since we'll assume that "home plate side of third base" means "between home and third") the key to answering your question is the location of the ball when it was touched. It does not matter where the player was located when it was touched. It only matters where the ball was when it was touched.

For instance, at umpire school, the instructors often ran a fair/foul drill. In that drill one instructor would through a high "pop-up" down the right field line and another instructor would catch it. We the students had to rule (1) fair/foul and (2) catch/no catch.

Now the instructors would try to do tricks. For instance, the catching instructor would intentionally put both of his feet in fair territory right up against the foul line, reach out with his left hand FULLY EXTENDED and make contact with the in-flight ball (over foul territory). In this drill, the instructors were trying to catch students who would rule "fair" (due to the fielder being in fair territory). The correct ruling is "FOUL" (because the ball was over foul territory when it was touched).

The same key applies in your scenario: where was the ball when it was touched?