25-Man Active Roster
40-Man Expanded Roster
The 40-man expanded roster includes everyone on the 25-man roster, as well as all the players signed to a Major League contract with the team. These players can be called up to join the 25-man active roster, but are not available right away to play in the game.
How Many Fielders (Defensive Players) Can There Be On The Field?
There can be a minimum of ten (10) and a maximum of thirteen (13) players on the field. There are always nine (9) defensive players (fielders) on the field, and anywhere from one (1) to four (4) offensive players (baserunners and batters).
How Many Batters/Baserunners (Offensive Players) Can There Be On The Field?
The number of offensive players on the field varies depending on how many runners are on base at a particular moment. If there are no baserunners, the batter is the only offensive player on the field. There can be up to three (3) baserunners, one on each base, plus the batter. This is when there would be a maximum of four offensive players on the field.
When people talk about the manager in baseball, they usually are referring to the field manager. He sits in the dugout and makes important strategic decisions about the game, including batting order/lineup, which player will fill each defensive position, pitching order/rotation, and in-game player substitutions. He is commonly referred to as the skipper.
The general manager works more on the administrative side. He oversees the building of the roster, including scouting/recruitment efforts, contract negotiation, and budget management. He is also in charge of employing and making changes to the coaching staff. The general manager is an extremely important component to the team, as his decisions affect the makeup and chemistry of the entire team. A team's long-term success relies on the prowess of its general manager.
Though not officially part of a team's roster of players, bat boys sit in the dugout and are an important part in helping the game run smoothly. After a batter gets on base, he drops his bat in the home plate area (since it'd be pretty hard to run the bases while holding a bat). It is then the bat boy's job to pick up the bat and put it back in its place in the dugout. Home plate umpires carry extra baseballs in a bag on their uniform; when their supply runs out, bat boys bring them fresh ones.
Each baseball player wears a number on his jersey that, among other players on the roster, is unique to only him. Sometimes, when a player is exceptionally great -- usually in a combination of skill, personality, and historical impact -- their number is retired by the team. This means that their number cannot be worn by any current or future player of the team, the number will always belong to them. It is a special way for teams to honor their brightest stars.
PRO TIP: Only one player's number is retired by every team in Major League Baseball: number 42, Jackie Robinson's number. Jackie Robinson was the first African-American player in the MLB. Every year on April 15, the anniversary of Robinson's first Major League game, every player in the MLB wears 42 in honor and memory of him.