From BR Bullpen
An ambidextrous pitcher has the very rare ability by a pitcher to throw both left-handed and right-handed. This would potentially allow a pitcher to always have the platoon advantage against a right-handed or left-handed batter or even a switch hitter. Against a switch hitter the pitcher needs to commit to a side and visually indicate it to the umpire and to the batter, while the batter can then choose from which side he wants to bat.
When ambidextrous pitcher Pat Venditte began pitching in the minor leagues in 2008, he caused the Professional Baseball Umpire Corporation to create a new rule regarding ambidextrous pitchers which later was adapted into the official baseball rules as Rule 8.01. It states that a "pitcher must visually indicate to the umpire, batter and runner(s) which way he will begin pitching to the batter."