After reading parts of the MLB Rule Book recently, I found there isn't anything that prohibits a fielder (First, Second, Short, or Third) from blocking their base - like a Catcher blocking home plate - to prevent a runner from returning safely to base.
When runners get a lead from First, what usually happens is that the First Baseman stretches as far as he can with his foot on the bag, and then tries to do a swipe-tag on the runner sliding into the bag. This almost never works. But once in a while, the runner will slide into the First Baseman's foot, never touch the base, and get tagged out.
As infrequent as this is, I've never seen it called Interference against the First Baseman.
If that's not Interference, why not block the base completely? Why give runners even half a chance to get back safely?
Runner's Interference is one of those things that are very hazily defined in the MLB Rule Book (the call involving A.J. Pierzynski of the White Sox a few weeks ago comes to mind).
Under what circumstances would Umpires call Interference against an Infielder for blocking his base? I've never seen it called against a Catcher when blocking home plate against a runner trying to score, with or without the ball.
I suppose this presumes the ball and the runner arrive at the base at approximately the same time, but the question remains - how much of the base is the fielder allowed to block?
If blocking the base is legal according to MLB rules, perhaps fielders could squat in front of their base and make the area available for the returning runner the size of a postage stamp. (Maybe First Basemen could wear Catcher's gear to prevent injuries on such plays).
But if it's legal, then maybe The Fridge could make a comeback as a late-inning defensive replacement! Urlacher would be even more intimidating! It might also make "rabbit runners" obsolete!