REFEREES have been shown green cards by managers as part of a new rule being trialled. Football fans are familiar with the yellow and red card rule, which has been prevalent in the beautiful game ever since the 1970 World Cup. One of them is being put to the test during the Under-20s World Cup in Chile. The Moroccan national football team's manager Mohamed Ouahbi showed the referee a green card. That new proposed card rule is being used to challenge a ref's decision and give more power to managers regarding VAR calls.