Surfing is a sport in which an athlete lies down or kneels on a surfboard and paddles to a place where the waves are suitable as a starting point. When the waves push the surfboard to slide, the athlete keeps the surfboard standing up in front of the wave crest, with the legs naturally open forward and backward (usually the balance leg is in front and the control leg is behind), the knees slightly bent, and the surfboard moves with the waves and glides quickly.