Offence
Quarterback
Receives the ball at the start of nearly every play, then decides in about three seconds whether to throw it, hand it off or run. He lines his team up, reads the defence's response, and sometimes changes the play on the fly.
Why they matter: The most important player in the sport by a distance. His formation — three wides, two tight ends, empty backfield — is the opening move in a chess game against the defence.
In football terms: Imagine Kevin De Bruyne, except he gets the ball at the start of every single attack and nobody else is allowed to start one.