Real Dictionary

quarterback
countable noun: In American football, a quarterback is the player on the attacking team who begins each play and who decides which play to use.

quarterback in American English
an offensive back who calls the play, takes the ball from the center, and then passes, hands off, etc.
to act as quarterback for (a team)
intransitive verb: to play the position of quarterback
noun: a back in football who usually lines up immediately behind the center and directs the offense of the team
transitive verb: to direct the offense of (a team)

quarterback in British English
noun: a player in American or Canadian football, positioned usually behind the centre, who directs attacking play