Depending on what events he does (Running, shot/disc, hurdles) you'd obviously want to capture him in the moment of those events. An easy and popular shot for sports is adding motion blur to the picture by panning the camera and following your subject as you take your picture.
This will allow your subject to stay in focus, while the rest of the background would be blurred.
Something like this :

(Taken from Wikipedia)
Otherwise, you can do a lot of closeups while in action...things like facial expressions and body movement.