rule 4.03:
4.03
When the ball is put in play at the start of, or during a game, all fielders other than the catcher shall be on fair territory.
(a) The catcher shall station himself directly back of the plate. He may leave his position at any time to catch a pitch or make a play except that when the batter is being given an intentional base on balls, the catcher must stand with both feet within the lines of the catcher’s box until the ball leaves the pitcher’s hand.
PENALTY: Balk.
(b) The pitcher, while in the act of delivering the ball to the batter, shall take his legal position;
(c) Except the pitcher and the catcher, any fielder may station himself anywhere in fair territory;
(d) Except the batter, or a runner attempting to score, no offensive player shall cross the catcher’s lines when the ball is in play.