The Americans are seeing red over the most controversial and consequential red card so far in the World Cup.While the United States celebrated a 2-0 win over Bosnia-Herzegovina, fans and players were angry and frustrated by a second-half red card that sent off star striker Falorin Balogun. It will sideline him for the next match against Belgium on Monday.The penalty, called after the referee watched a video replay, ignited debate over whether it was too harsh and whether other players, most notably Argentina’s Lionel Messi, have unfairly avoided similar punishment.

What is a red card and how to earn oneRed cards are the most serious form of punishment in a referee’s pocket. A red card does more than just send a player out of the game. It also means the team can’t replace them and must play shorthanded. The ejected player is also suspended for the next match — and sometimes longer depending on the offense.The red and yellow card system of discipline was invented after the 1966 World Cup by former referee Ken Aston, who came up with the color-coded level of discipline while stopped at a traffic light. “I thought, ‘Yellow, take it easy; red, stop, you’re off’,” said Aston, who died in 2001.Much is left to the referee’s discretion in the heat of play. A player who receives a second yellow card during a game is automatically ejected with a red card. Direct red cards usually result from more serious offenses, such as dangerous tackles and violent play.