Instant replay

Instant replay (as it relates to ice hockey) originally was the use of showing key plays during a hockey game such as goals, close calls, or controversial calls (ie offside, who was the last one to touch the puck in the crowd in front of the next on a long distance screen shot, hard hits, cheap shots on another player, did the puck beat the siren across the goal line, or something unusual during the course of play during a hockey game).
==History of instant replay==
During a 1955 Hockey Night in Canada broadcast on CBC Television, producer George Retzlaff used a "wet-film" (kinescope) replay, which aired several minutes later. Videotape was introduced in 1956 with the Ampex Quadruplex system. However, it was incapable of displaying slow motion, instant replay, or freeze-frames, and it was difficult to rewind and set index points.
The end of the March 24, 1962 boxing match between Benny Paret and Emile Griffith was reviewed a few minutes after the bout ended, in slow motion, by Griffith and commentator Don Dunphy. In hindsight it has been cited as the first known use of slow motion replay in television history.
CBS Sports Director Tony Verna invented a system to enable a standard videotape machine to instantly replay on December 7, 1963, for the network's coverage of the US military's Army–Navy Game. The instant replay machine weighed .
 After technical hitches, the only replay broadcast was Rollie Stichweh's touchdown. It was replayed at the original speed, with commentator Lindsey Nelson advising viewers "Ladies and gentlemen, Army did not score again!" The problem with older technology was the difficulty of finding the desired starting point; Verna's system used audio tones activated as an interesting event unfolded, which technicians could hear during the rewinding process.
Replay from analog disk storage was tried out by CBS in 1965, and commercialized in 1967 by the Ampex HS-100, which had a 30-second capacity and freeze frame capability.
==Modern Era==
As technology improved the possibility of reviewing calls by game officials became reality. The speed of play in ice hockey made instant replay a necessity for getting calls correct. Along with going to a four person on-ice officiating crews in 2001, instant replay has help shape the game of the modern game of hockey in terms of coaching decision making. A 90 mile/145 kilometres per hour shot moves at about 132 feet/40 metres per second and is in and out of the goal in about 1/100th of a second and is sometimes undetectable to the human eye. The NHL require arenas to install fixed cameras in certain positions such as high above the nets at each end to detect if a puck went in the net.
Penalties have been reviewed such as high sticking penalties and had the situation clarified as sometimes a player was hit by a teammate's or even their own stick which would negate a penalty against the other team.
===Ice hockey officiating===
The NHL uses what is called the Situation Room or War Room at the league offices in Toronto where an assigned officials are responsible for one game. 
The video goal judge reviews replays of disputed goals. As the referee does not have access to television monitors, the video goal judge's decision in disputed goals is taken as final. In the NHL, goals may only be reviewed in the following situations: puck crossing the goal line completely and before time expired, puck in the net prior to goal frame being dislodged, puck being directed into the net by hand or foot, puck deflected into the net off an official, and puck deflected into the goal by a high stick (stick above the goal) by an attacking player. The video goal judge also reviews replays to establish the correct time on the game clock. All NHL goals and time remaining on the game clock are subject to review, and although most arenas have a video goal judge, often officials in the Situation Room (also known as the "War Room") at the NHL office in Toronto make the final decision.
Replays have been done as the game play is going on and the replay official has notified the timekeeper that a goal has been scored and usually the arena's end of period siren is activated to stop play so that the on-ice officials are notified a goal has been scored. 
There is a red light above the officials box which in NHL arenas is located between the penalty boxes. If the situation room is reviewing a goal that has some possibility of being disallowed that light will go on to tell the official to hold off on restarting play until the goal is confirmed (good goal) or disallowed.
====Review challenges====
Beginning in the 2015-16 NHL season, instant replay reviews have been expanded to include a coach's challenge. Each coach receives one challenge per game, which requires the use of a timeout. Coaches may only challenge over situations whether the goal should have been disallowed because of goaltender interference or an offside, or whether a goal disallowed because of goaltender interference should be allowed instead. The challenging team retains its timeout and its challenge after every goaltender interference call that has been overturned. There are two situations that happen when a challenge is upheld:
*If an offside review is upheld, the challenging team receives a minor penalty for delay of game.
*If a goaltender interference review is upheld, the challenging team loses its timeout.
Challenges are not allowed during the final minute of regulation, as well as at any point during overtime. In this situation, officials in the Situation Room reviews all instances where the puck entered the net, and then determines the final ruling. However, for reviews that take place during coach's challenges, the on-ice officials determine the final ruling.
====Announcing of decisions====
The referee will announce the result of the review to the players, arena crowd, and television spectators with terms such as the 
1. The play stands as called (the video is inconclusive enough to overturn the call), 
2. The ruling is confirmed (by the video)
3. The goal is disallowed due to a rule infraction (such as a high stick, the puck is kicked or thrown in the net, the puck went out of play prior to the goal) which is further explained by the referee
If the review was the result of a coaches challenge points are clarified such as a team losing/keeping their time out or a two minute minor bench penalty for the unsuccessful challenge for delay of the game.
An official may also wave off a goal when they lost sight of the puck under a pile and are under the impression that the goaltender has frozen the puck with either their body or equipment. The term for this situation is "dead in the head" as the official is stopping play and there is an (ever so brief) delay between that instant and the whistle being blown and play is stopped in the official's opinion. Depending on how the play has gone the situation may not be subject to a longer review as the referee may talk with the situation room official and say when he lost sight of the puck and if it was before puck went in the net no further review is conducted as the referee losing sight of the puck is legitimate grounds to stop play.
Category:Terminology