I'm kind of surprised how many people are so butthurt about this. My local league allows it, I don't do it and I've never seen anyone do it in a sanctioned tournament. Really who cares, its a disadvantage to the base runner and has no other impact on the play.
Call it a ***** rule if you like but it is safer. Even if the runner moves just 5 feet off the base they are marginally farther from the hitter. Most of the times I've seen this happen the runner also takes a couple steps towards the outfield. For those who say its only 5 feet farther it doesn't matter, then let me ask why a bunch of associations have considered pushing bases back 5 feet for safety. Last there are less hard hit balls hit 5 feet into foul territory then there are on the 3rd base line just based on where players are trying to hit the ball.
Seriously stop the whining, as a fielder it has almost no impact on the game and it makes the game marginally safer.
Hows this for a scenario....player is 4 feet off the base in foul ground and gets drilled in the head with a foul ball. Guess who gets sued. The league, the umpire, the LD, the town. Now as an umpire or LD you're screwd. If they get hit while on the bag, they have no course of action to sue. They have the right to sue, but they won't get far.
Once you start ignoring the rules of your association that association's insurance pretty much becomes void.
This makes no sense, the runner was given the option to move into foul territory and did it on their own free will. The odds of the league getting sued here are just as likely as they would for getting sued for not requiring helmets or some other stupid unreasonable reason that an injured person would sue.