Football is played between two teams that consist of the same number of players. The object of the game is for the offensive side to move the ball into the endzone via passing and running, resulting in a touchdown.
Football is not played continuously; instead, it is split up into "downs." The offense is given four downs in football, during which they must move the ball either into the endzone or beyond the first down marker. The first down marker is placed 10 yards away from where the ball is originally spotted when the offense's possession begins. Moving the ball beyond the first down marker results in a new set of downs; however, if the offense fails to acquire a new first down with four downs, then they turn the ball over to the other team.
A play begins with the snap of the ball from the center to the quarterback. The spot at which the ball is snapped is referred to as the "line of scrimmage": an imaginary line that extends horizontally across the field from where the ball is spotted. Neither the defense nor the offense is allowed to cross the line of scrimmage prior to the snap of the ball, as doing so results in a penalty. Forward passes are only allowed by the offense when the ball is thrown from behind the line of scrimmage; the ball may only be lateraled horizontally or backwards after it has been advanced beyond the line of scrimmage.