Let me settle this dabate between Bob T and Doctor Jackson once and for all. In a way your both right. A pinch hitter or runner, or any substitution for that matter does not have to be announced over the PA system. To make a substitution, the manager must first go to the umpire-in-chief (head umpire) and OK the switch. The umpire will make note of the switch on his lineup card but he is not obligated to announce it. He may simply notify the other manager of the change or the PA announcer will announce the change (the PA announcer may not announce any changes without instruction from the umpire. What actually happens is the umpire will notify the official scorer, usually by way of hand signals, then the scorer will tell the PA announcer.) If the umpire wishes not to announce the change, the change will become official when: a)if the player is a pitcher, he takes his place on the pitcher’s plate, b)if a batter, he takes his place in the batters box, c)if a fielder, he reaches the position usually occupied by the fielder he has replaced, and play commences, and c)if a runner, he takes the place of the runner he has replaced. This is all according to the “Official Rules of Major League Baseball” so don’t argue.