Instant replay or action replay is a video reproduction of something that recently occurred which was both shot and broadcast live. The video, having already been shown live, is replayed in order for viewers to see again and analyze what had just taken place. Some sports allow officiating calls to be overturned after the review of a play. Instant replay is most commonly used in sports, but is also used in other fields of live TV. While the first near-instant replay system was developed and used in Canada, the first instant replay was developed and deployed in the United States.
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 utilized 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 1,300 pounds (590 kg). 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.
Instant replay has been credited as a primary factor in the rise of televised American football, although it was popular on television even before then. While one camera was set up to show the overall "live" action, other cameras, which were linked to a separate videotape machine, framed close-ups of key players. Within a few seconds of a crucial play, the videotape machine would replay the action from various, close-up angles, in slow motion.
Prior to instant replay, it was almost impossible to portray the essence of an American football game on television. Viewers struggled to assimilate the action from a wide shot of the field, on a small black-and-white television screen. However, as Erik Barnouw says in his book, "Tube of Plenty: The Evolution of American Television", with replay technology, "brutal collisions became ballets, and end runs and forward passes became miracles of human coordination". Thanks in large part to instant replay, televised football became evening entertainment, perfected by ABC-TV's Monday Night Football, and enjoyed by a wide audience.
Marshall McLuhan, the noted communication theorist, famously said that any new medium contains all prior media within it. McLuhan gave Tony Verna's invention of instant replay as a good example. "Until the advent of the instant replay, televised football had served simply as a substitute for physically attending the game; the advent of instant replay – which is possible only with the television – marks a post-convergent moment in the medium of television".