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?

Red 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.

Under FIFA rules, “Any player who lunges at an opponent in challenging for the ball from the front, from the side or from behind using one or both legs, with excessive force or endangers the safety of an opponent is guilty of serious foul play.”

Balogun’s red card sparked a debate over whether the foul should have been deemed intentional or just a hard tackle that would have justified a warning with a yellow card.

“It never was intentional,” U.S. coach Mauricio Pochettino said. “If the intention is to damage the opponent, OK, I understand. But that never was. It was a normal action in football that you are fighting for the ball and your feet land.”

Video review

The referee has the challenge of watching all the action all the time. In a tangle of bodies, something could be missed. FIFA introduced the use of Video Assisted Review, or VAR, in the World Cup in 2018.

In Balogun’s case, Brazilian referee Raphael Claus didn’t initially signal a card. But an order from the VAR officials to review the replay in slow motion resulted in the red card.

That sparked another debate of whether the play looked worse and more intentional in slow motion.

Former France striker Thierry Henry, now a studio analyst for the World Cup with Fox Sports, criticized the red card.

“You need to have some common sense,” Henry said. “Where is the player supposed to put his foot there in that situation?”

There is no path to appeal. Balogun has to sit one out

As it stands, Balogun will miss the next game but could return for the quarterfinals if the U.S beats Belgium to advance.

There is no appeal for a red card suspension unless FIFA assesses a penalty of more than one game. FIFA could increase the ban if it believes the challenge deserves a harder punishment.

Portugal star Cristiano Ronaldo avoided missing games in the World Cup after a serious red card incident in qualifying. FIFA instead determined two games of a three-match ban would be deferred during a one-year “probationary” period.