From BR Bullpen
A player is a person who is taking part in a baseball game for one of the competing teams. The term may refer to a fielder (including the pitcher), to the batter or to a baserunner. In certain cases, the term may also include substitutes who have not yet entered the game. Other personnel such as the umpires, the manager and coaches or the official scorer are not considered players.
The term is used at various points in the official rules of baseball. For example, a batted ball that hits a player is treated differently than a ball that hits another person on the field.