RulesMLB Umpire Manual
PITCHER CHANGING DEFENSIVE POSITIONS
Rules 5.10(d) Comment, 5.10(g): The purpose of this Comment is to prohibit a player from being a substitute for a pitcher more than once in the same inning. Thus, a player who starts (or enters the game during) an inning as a pitcher may substitute for any position(s) afterwards; however, he may not return to…
RulesMLB Umpire Manual
RESTRICTIONS ON PITCHERS WARMING UP
Rule 5.07(b): The home club pitcher may not warm up on the mound prior to the start of the game. To do otherwise could give the home club pitcher some advantage, and because pregame practice conditions should be equal for both starting pitchers, both pitchers should warm up where pitchers normally warm up. A game…
