noun

• (American football, Canadian football) An offensive back whose primary job is to pass the ball in a play.
  "Standing 6-foot-6, 237 pounds, Herbert’s size and arm strength are consistent with a prototypical N.F.L. quarterback, and he led the Ducks to a Pac-12 championship and a victory at the Rose Bowl in January with not much talent at receiver."
• (American football, historical) An offensive back who receives the snap (hike) and then blocks the defense from crossing the line of scrimmage; a blocking back.
• (rugby football, historical) A position just behind the forwards, or one who plays this position.

verb

• (American football, transitive) To play the position of quarterback.
• (figuratively, by extension, transitive) To lead a team or group; to be primarily responsible for some group project or activity.
  "Wayman's major responsibility is to quarterback the team, coordinating business development, project scheduling and management and quality control."