Flags are used in many sports to signal and communicate. In australia, yellow and red flags on the beach indicate swimming conditions. There are no universal standards, but in auto racing a green flag generally means start, but in auto racing a green flag genrrally means start, yellow means caution, red means stop, and a black and white checked flag means the race is finished. American football uses a yellow flag when a rule is broken, while Canadian football uses an orange flag. Flags are not restricted to the field. Many sports teams have their own flags and fans wave them to show support for their favorite team