作者loveless.

根據國際籃球規則(FIBA Official Basketball Rules)

本來2006年的規則中，除非有醫生證明許可，否則球衣內不可穿著任何形式的Ｔ恤，若經允許穿著，Ｔ恤亦須與球衣相同顏色。
2006 Art. 4.3.1
T-shirts, regardless of style, may not be worn under shirts unless the player has written medical permission. If such permission has been granted, the T-shirt must be of the same dominant colour as the shirt.

後來2008年的規則中將有關Ｔ恤的敘述刪除，即無論任何原因，球衣內皆不得穿著任何Ｔ恤。
2008 Art. 4.3 Uniforms

The provision that T-shirts may be worn by players under their game uniforms is not valid anymore.

當然表演賽，特別賽...非FIBA規定的賽制不用按照FIBA的規則也可以。