uniform number; shirt number; squad number
The number on the back of a player's uniform in sports such as baseball, soccer, basketball, and rugby.
彼の背番号は10番だ。
His uniform number is 10.
引退した選手の背番号を永久欠番にした。
They retired the uniform number of the player who retired.
He wears uniform number 7.
That player's uniform number was retired.
He played bearing the legendary uniform number.