Can a player come back into a baseball game after being taken off?

• Nine at all times: each team must always have nine eligible players in the game.
• No return: a player removed for a substitute cannot re-enter.
• When: any player other than the pitcher or DH may be replaced whenever the ball is dead.
• Batting place: the substitute bats in the replaced player's place.
• Pinch-hitter and pinch-runner: substitutes who bat or run for a player in the line-up.
• No courtesy runners: a player already in the batting order may not run for a team-mate.
• A new pitcher: must pitch until the batter then at bat "is put out or reaches first base", or the side is out.
• Injury: a pitcher who is injured or ill may be replaced immediately.
• Unannounced: a substitute who is not reported becomes legal on taking up the position, and plays made stand.
• Warm-up: a substitute for an injured fielder gets five warm-up throws.
• Still useful: a withdrawn player may sit on the bench, warm up pitchers and act as a base coach.
• Trying to return: the umpire has the player removed. Any play made while they were in still counts.

The glossary has the team, the pitcher, the bullpen, the closer, the designated hitter and the batter.

The no-return rule makes every substitution a real decision: bringing in a pinch-hitter costs the player replaced for the rest of the day. The one-batter rule for pitchers stops a manager from changing pitcher again and again within one turn at bat to gain a match-up and slow the game.