Red and yellow cards were invented because of a World Cup language barrier

The card system that every football fan takes for granted — yellow for a caution, red for a sending-off — was invented because of a communication disaster at the 1966 World Cup. In the quarter-final between England and Argentina, English referee Ken Aston struggled to communicate his decisions to players who spoke different languages. The confusion was so bad that some players didn't even know they'd been cautioned.

Driving home afterward, Aston stopped at a traffic light and had his eureka moment: yellow means caution, red means stop. He proposed the card system to FIFA, and it was first used at the 1970 World Cup in Mexico — the same tournament that introduced color television.

The beauty of the system is its universal clarity. A referee in Japan showing a red card to a Brazilian player is immediately understood by everyone in the stadium and watching on TV. No translation needed. The cards have become so iconic that they've been adopted by other sports, and "getting a red card" has entered everyday language as a metaphor for being expelled.