When photographing most sports, a key rule is to include the eyes of the subject. Sure, that is not always possible if a skater is 25-feet in the air, or a surfer 10-feet back in the tube. But when given the chance it is the face that registers most of the emotion of an athlete, and the eyes specifically that tell all.
By keeping alert for the moments when an athlete’s eyes may light up (or go downcast) you’ll have images that tell a story. Shooting someone’s back doesn’t seem tend to have the same effect.