Footballing means relating to football. You almost always put it in front of another word, in British sports writing: a footballing nation (a country that lives and breathes football), footballing skills, a footballing family, a footballing injury. It does not mean “playing football at this moment” — that is just playing football. Americans rarely use it; they would say soccer, or use football as a noun. In this word, football is the sport with a round ball, the one Taiwan calls 足球, not American football.

足球的、與足球有關的。這是英國報紙用語；台灣一般直接說「足球」就好，例如 footballing nation 就是足球強國、足球氣息很濃的國家。