Badminton, like tennis, is a racket sport that is played by either two players or two teams of two players each. The object is for you or your team to get to 21 points first. You score a point whenever you successfully serve the shuttlecock and your opposing team commits a fault, which means that the team fails to appropriately return the shuttlecock.
Assuming one cares for their teeth by brushing regularly, saliva may smell bad because there are millions of bacteria present in the mouth. Bad smelling saliva or breath can be indicative of a tooth abscess, or a systemic illness such as diabetes.
One is that saliva helps kill bacteria found in your mouth, and the other is that saliva helps you digest food particles caught in your teeth and other areas of your mouth. If there is no longer enough saliva in your mouth because of caffeine, then the bacteria that cause bad breath will grow out of control.