<P> Replay reviews are only utilized at the college level and above . The National Federation of State High School Associations (NFHS) establishes the rules for most high school and youth organizations in the United States, and the rules of the NFHS do not permit replay reviews even when the equipment exists to enable the practice . In those leagues that utilize replay reviews, there are restrictions on what types of plays can be reviewed . In general, most penalty calls or lack thereof cannot be reviewed, nor can a play that is whistled dead by the officials before the play could come to its rightful end . </P> <P> American and Canadian football leagues vary in their application and use of instant replay review . </P> <P> The National Football League first adopted a limited Instant Replay system in 1986, though the current system began in 1999, bringing in the opportunity to "challenge" on - field calls of plays . The current system mirrors a system used by the now defunct USFL in 1985 . Each coach is allowed two opportunities per game to make a coach's challenge . Before the 2004 NFL season, the instant replay rule was slightly changed to allow a third challenge if both of the original two challenges were successful . </P> <P> A challenge can only be made on certain reviewable calls on plays that begin before the two - minute warning and only when a team has at least one time - out remaining in the half . Up until the 2005 season, coaches could signal a challenge via an electronic pager, now used only by the replay assistant . The coaches now throw a red flag onto the field, indicating the challenge to the referees . This red flag was originally the "backup plan" if the pager were to fail, but it has become the more popular option among NFL coaches to signal a replay request . </P>

When was instant replay first used in the nfl
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