In rugby union, a yellow card temporarily suspends a player for 10 minutes.
The referee shows a yellow card for an offence serious enough to require temporary removal but not necessarily permanent expulsion. The player leaves the field and cannot be replaced during the suspension, so the team plays with 14 players for the relevant period.
Yellow-card offences can include repeated infringements, dangerous or cynical foul play, and deliberate acts that prevent an attacking opportunity. The precise decision depends on the laws, match circumstances and the referee’s judgement.
A red card is more severe: it sends the player off permanently. Modern competitions may also use a review or replacement process for certain red-card incidents, but that does not change the basic distinction between a temporary yellow-card suspension and a permanent red-card dismissal.