In baseball, the field manager (commonly referred to as the manager) is an individual who is responsible for matters of team strategy on the field and team leadership. Managers are typically assisted by between one and six assistant coaches, whose responsibilities are specialized. A manager is essentially equivalent to the head coach in other North American professional sports leagues.
Manager (baseball) Wikipedia
The manager chooses the batting order and starting pitcher before each game, and makes substitutions throughout the game – among the most significant being those decisions regarding when to bring in a relief pitcher. How much control a manager takes in a game's strategy varies from manager to manager and from game to game. Some managers control pitch selection, defensive positioning, decisions to bunt, steal, pitch out, etc., while others designate an assistant coach or a player (often the catcher) to make some or all of these decisions.
Some managers choose to act as their team's first base or third base coach while their team is batting in order to more closely communicate with baserunners, but most managers delegate this responsibility to an assistant. Managers are typically assisted by two or more coaches.
Typically, the title of "manager" is only used in professional baseball, with the title "head coach" used at other levels of play.
In many cases, a manager is a former professional, semi-professional or college player. Many current and former managers are former catchers which include Mike Matheny, John Gibbons, Brad Ausmus, Joe Torre, Mike Scioscia, Bruce Bochy and Joe Girardi.
The manager's responsibilities normally are limited to in-game decisions, with off-the-field and roster management decisions falling to the team's general manager. The term manager used without qualification almost always refers to the field manager (essentially equivalent to the head coach in other North American professional sports leagues), while the general manager is often called the GM.
Major League Baseball managers differ from the head coaches of most other professional sports in that they dress in the same uniform as the players and are assigned a jersey number. The wearing of a matching uniform is frequently practiced at other levels of play, as well. The manager may be called "skipper" or "skip" informally by his players.