(a) If no announcement of a substitution is made, the substitute shall be considered as having entered the game when—
(1) If a pitcher, he takes his place on the pitcher’s plate;
(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.
(b) Any play made by, or on, any of the above mentioned unannounced substitutes shall be legal.
In 2008, the Los Angeles Dodger's Mark Sweeney entered the batter’s box as a pinch hitter for Pablo Ozuna in the 8th inning. Dodger manager Joe Torre changed his mind about hitting Sweeney, and asked home plate umpire Chris Guccione whether Sweeney had been announced. Guccione responded that Sweeney was not yet in the game. However, unknown to Guccione, Sweeney took his position in the batter’s box. When Torre sent pinch hitter Jeff Kent to bat, St. Louis Cardinals manager Tony La Russa objected. Crew chief Tim Welke correctly ruled that Sweeney had entered the game and was subsequently replaced by Jeff Kent. The Dodgers protested the game.