How do you play cricket?

Because a single ball is used for an extended period of play, its surface wears down and becomes rough. The bowlers will polish it whenever they can - usually by rubbing it on their trousers, producing the characteristic red stain that can often be seen there. However, they will usually only polish one side of the ball, in order to create 'swing' as it travels through the air. They may apply natural substances (i.e. saliva or sweat) to the ball as they polish it, but any other material is illegal.