Softball is played with nine starting players. Depending on the league rules, the number of reserve, or bench, players varies. A coach can substitute the players who do not start the game for starting players. The rules for substitution vary depending on which starting player is being substituted, what position she plays, and whether the game is slow-pitch or fast-pitch softball.
A coach can substitute a pinch runner into the game for a starting player. The only way that a pinch runner can go into the game for a starting player is if that starting player has gotten on base. The pinch runner’s job is strictly to run the bases, usually because the starting player is a slower runner.
Starting players who have been substituted out for a pinch runner can re-enter the game in their defensive position, such as shortstop. Additionally, in fast-pitch softball, a starter can re-enter the game as an offensive player as long as she enters in the same position in the batting order that she started the game. So if she started as the fourth batter, she has to wait until it is the fourth batter’s turn. If the starting player gets on base again and the coach takes her out for a second time for a pinch runner, the starting player may not play the rest of the game.
When a bench player leaves the game so that a starting player can go back in, the bench player is ineligible to play the rest of the game. There is something known as a defensive swap, however, where players can switch positions with each other on defense. If both players are starting players, they can switch positions as many times as they want without any eligibility consequences.
A courtesy runner is different than a pinch runner. A coach can substitute a courtesy runner at any time for a pitcher or catcher whenever those two players reach base. The pitcher or catcher can re-enter the game without any penalty, and the coach can substitute the courtesy runner back in for a pitcher or catcher as many times as necessary. The only exception is that the same courtesy runner can’t be used for both a catcher and a pitcher.
A flex player can enter the game as a designated batter for a pitcher, but it is not considered a substitution. The team must notify the umpire, however, if a designated batter will hit for a pitcher.