The (unwritten) rule we are talking about is a "courtesy" clause, secretly attached to every baseball game that binds, Players & Managers to this 'rule':

Unwritten Rule 23.2D: "If you are kicking the crap out of an opponent, you willingly agree (Managers) to unwillingly (Players) "Give Up At-Bats" to help finish the ballgame. The trailing team is allowed to bring in a position player to pitch, in which you must try even less... Oh and absolutely, NO SWINGING ON 3-0 PITCHES, unless you make an out." 

PENALTY: Managers are allowed to openly criticize you for being successful/producing and the other team gets to throw at you in your next at bat against them. (See Examples Below)...