The reason for having nine innings in a game of baseball is unknown, but there is speculation that the number was determined based on the number of players. The tradition of a nine-inning baseball game began in 1857.
Baseball's first known rules came from the Knickerbocker Club in 1845. However, a reworking of the rules of baseball in 1857set the number of players and innings at nine.
Forms of the game of baseball date back to records from the mid-1300s in France, though the first record of the game dates to 1744 in Britain. Baseball became popular in the United States in the late 1700s to mid-1800s.
The game of baseball is not timed, unlike other sports. Each team will take the field and go to bat nine times, which become the innings that determine the length of the game.