The game of baseball is played in nine innings, cats are fabled to have nine lives, the U.S. Supreme Court has nine justices and there are nine ladies dancing in "The Twelve Days of Christmas". There were nine planets in the solar system until the demotion of Pluto.
The rules of baseball underwent a thorough revision in 1857 that shaped the parameters of the modern game including having nine innings in a game, nine players on a team and ninety feet between bases. There is one pitcher, a player to cover every base, a catcher, a shortstop to cover the distance between the bases and three outfielders.
The myth of the cat with nine lives comes from a ritual in Medieval Europe of throwing cats from tall towers. One legend is told of Baldwin III, Count of Ypres, who dropped many cats from a tall tower in the town, most of which survived.
The U.S. Supreme Court has had nine judges since the Judiciary Reorganization Bill of 1937, proposed by President Franklin D. Roosevelt. Roosevelt argued that the Court wasn't up to the job due to the age of its members and added one new justice for every member over 70 years old.
In "The Twelve Days of Christmas," nine ladies dancing represent the Nine Choirs of Angels or the nine fruits of the Holy Spirit.
There were nine planets in the traditional model of the solar system until the International Astronomical Union demoted Pluto to a dwarf planet in 2006.