Is describing football players with certain descriptions considered backbiting, and will I be held accountable for that if they are People of the Book?

Mentioning a person with what they dislike in their absence is forbidden backbiting (gheeba), which is not permissible except for a legitimate purpose. There is no distinction in this between a Muslim and a non-Muslim from among the peaceful People of the Book. As for a warring disbeliever, backbiting them is not forbidden. If the aforementioned players are not belligerent, then backbiting them is not permissible.