Pitcher takes the mound and appears to be taking signs, but has back foot behind pitcher’s plate. Pitcher then throws to base to pick off runner. Ump says pitcher was throwing as fielder because he hadn’t engaged the pitcher’s plate yet.
In another instance, Pitcher takes the mound in set position, ball and hand in glove, but pivot foot behind the pitchers plate. Pitcher then moves pivot foot in front of pitcher’s plate in contact with the rubber. Ump says pitcher did nothing wrong.
In the first example, it is illegal for the pitcher to take signs from the catcher when not engaged with the pitcher’s plate. This is a balk. There is, however, no balk simply for throwing to a base from behind the pitcher’s plate. It is an important distinction because, as a “fielder,” a ball thrown out of play would be a two base award. If the pitcher were engaged with the pitcher’s plate when he threw out of play, the award would only be one base.
In the second example, I see this a lot. It is difficult for the plate umpire to see this, but it is legal as long as pitcher has the ball, and the team is not trying a hidden ball trick. If the pitcher took the same stance without the ball, it would be a balk.