A yellow card was upgraded to a red during a Wales game for the first time due to a "high danger" act committed by Japan U20s' captain.
It was announced prior to the World Rugby U20 Championship kicking off that the new system would be in place for all games, with reports saying it could be implemented at this year's Rugby World Cup too.
The TMO bunker system allows a yellow card to be upgraded to red. Players who commit a definitive red card offence can be sent off immediately, but for incidents which require closer attention, referees can send them to the sin bin for an initial 10 minutes while the incident is reviewed off the field. It allows the game to be sped up, and has already been trialled in Super Rugby this season.
