As soon as a player touches a ball in foul territory it is foul (doesn't matter where any parts of the player's body are). The only reason to run out a foul pop-up is because sometimes they have ridiculous amounts of spin and they could land 10 or more feet foul and still roll into fair territory before someone touches them. However, this only applies if the ball has not travelled beyond first or 3rd base. If a ball has clearly travelled beyond the bases and is clearly foul with no chance of hooking fair, then there is no reason to run it out.
|