The phrase "to become a member of a football team" in Engpsh is "to join a football team."
The phrase "to join" means to become a part of or to unite with something. In this case, it refers to the action of joining a football team as a player.
Examples in Engpsh with Chinese translation:
I want to join the school football team. (我想加入学校足球队。)
He joined the professional football team last year. (他去年加入了职业足球队。)
She is trying out for the football team next week. (她下周要试训足球队。)