What is a yellow card? Yellow and red cards in soccer operate much like the yellow and red lights on a traffic light. Yellow serves as a warning to ... or unsportsmanlike behavior during a match.

Fans attending local high school sports games could also get yellow and red cards if ... "A simple warning, a warning the rest of the crowd might see, to get that behavior change we're looking ...

Basically, it's a foul, and the degree of which will dictate whether it's a warning to ... will present a yellow card in order to caution a player for unsporting behavior, repeated infringement ...