A football game is consists of four quarters and a timekeeper officiates their duration. In professional level, each quarter consist of 20 minutes of play, with the clock being stopped for instances such as scores, the ball going out of bounds, or at the umpires discretion (ex: for serious injury). Lower grades of competition might employ shorter quarters of play. The umpire signals time-off to stop the clock for various reasons like, the player in possession being tackled into stagnant play.
Time resumes when the umpire signals time-on or when the ball is brought into play. Due to stoppages, the quarter extends to approximately 5-10 minutes beyond the 20 minutes of play. 6 minutes of rest is allowed before the second and fourth quarters , and 20 minutes of rest is allowed at half time.
The official game clock is available only to the timekeeper’s and it is not displayed to the players, umpires or spectators. The only public knowledge of the game time is when the timekeeper sounds a siren at the start and end of each quarter.
Coaching staff may monitor the game themselves and convey information to players via on-field trainers or substitute players. Broadcasters usually display an approximation of the official game time for television audiences.