A player or players may be substituted during a game at any time the ball is dead.
A substitution is completed and the player is considered as having entered the game when the manager or his designee notifies the plate umpire of the substitution. If no such notification is given to the umpire or after notification no announcement is made, the player shall be considered as having entered the game when:
(1) If a pitcher, he takes his place on the pitcher’s plate prior to delivering a pitch (preparatory or otherwise);
(2) If a batter, he takes his place in the batter’s box;
(3) If a fielder, he reaches the position usually occupied by the fielder he has replaced, and play commences;
(4) If a runner, he takes the place of the runner he has replaced.
Umpires should confirm all substitutes from the manager and inform the opposing manager of all substitutes.
NOTE: If a pitcher has been brought into the game but has not faced one batter (or retired the side) when the game is stopped for weather, such pitcher may, but is not required to, continue pitching when the game is resumed.
Refer also to Official Baseball Rule 5.10 for additional information concerning