Real Dictionary

baseball
countable noun: A baseball is a small hard ball which is used in the game of baseball.
uncountable noun: In America, baseball is a game played by two teams of nine players. Each player from one team hits a ball with a bat and then tries to run around three bases and get to the home base before the other team can get the ball back.

baseball in American English
a game (esp. hardball (sense 1) hardball (sense 1a)) played with a bat and a ball by two opposing teams of nine or ten players on a field with four bases: each team takes turns batting against the opponent's pitcher and tries to score more runs than the o
noun: a game of ball between two nine-player teams played usually for nine innings on a field that has as a focal point a diamond-shaped infield with a home plate and three other bases, 90 ft. (27 m) apart, forming a circuit that must be completed by a base run

baseball in British English
noun: a team game with nine players on each side, played on a field with four bases connected to form a diamond. The object is to score runs by batting the ball and running round the bases