1) The referee maintains the tempo of the game, communicates with other officials, sets the line of scrimmage, and begins play by blowing the whistle and starting the play clock. 2) After announcing the down and line to gain, the referee blows the ready for play whistle to signal the offense has 25 seconds to snap the ball before a delay of game penalty. 3) If a foul occurs, officials blow their whistle twice to get the referee's attention and quickly report the foul details to the referee, who then enforces the penalty.