MLS became one of the first leagues in the world to adopt Video Review beginning in Week 22 of the 2017 MLS season.
The Video Assistant Referee (VAR), the new fifth member of the officiating crew, is constantly checking all plays using every video angle available from the match broadcaster.
The VAR alerts the head referee to potential clear and obvious errors in four match-changing incidents: (1) goals, (2) penalty kicks, (3) direct red cards and (4) cases of mistaken identity.
Only the head referee can initiate a Video Review by making the Video Review signal (TV box sign). If video evidence is inconclusive, the original on-field decision will stand. The final decision always rests with the head referee.