After the two-minute warning, the responsibility of calling reviews shifts from coaches to the replay assistant in the booth. Sometimes those decisions can directly determine the outcome of the game. The replay assistant only has the time between plays to decide whether to order review. Even if a call is not overturned, a decision to review can affect a team's momentum at a critical juncture.
The replay assistant is part of the officiating team. He participates in the review process throughout the game, but can't initiate a review until the two-minute warning has passed. If he then sees a call that appears questionable on replay, he activates a vibrating buzzer worn by the referee.
To make a speedy review possible, high-definition signals from all cameras are sent by fiber optic cables to the replay booth. There they are recorded on two computer servers and cued up by a technician. A video operator transfers relevant replays to a monitor, which the replay assistant looks at to decide whether a review is called for. A communicator watches the action on field, announcing to the replay assistant whether play has resumed [source: Steelersfever.com].
If the assistant calls for a review, the replay signal seen by the referee is sent to the two shielded monitors on the sidelines. In outdoor stadiums, a third is placed in a runway in case of bad weather.
Review rules are now here to stay. Most agree that they have helped make the game fairer. But no matter how efficient the technology, replays will never eliminate all controversies.
For example, during a November 1989 Packers-Lions game, Green Bay quarterback Don "Magic" Majkowski threw an apparent touchdown to win 14-13. But field officials ruled that he had stepped over the line of scrimmage before throwing: no touchdown. Review by the assistant in the booth overruled the call and awarded the touchdown. It became known as "Instant Replay Game." Because the truth was in the eye of the beholder, fans have argued the call ever since [source: Sorgi].
Read on for more information about NFL review rules.