You have to know what you are photographing. If you photograph an athlete in action you have to show why that moment is a great moment. You need to put the photo into perspective.
If you understand a certain movement, trick, it’s clear to you why it’s a great movement. You only will understand it if you understand the sport itself, the tricks, the style, everything.
Of course everybody can make a good photo of a skateboarder! But it’s all about the composition. I recently saw a classic mistake in a daily newspaper with a photo about skateboarding. The photographer zoomed in as much as possible and with the skills he had he created a perfect photo by the rules. Tack sharp, good colors, rule of thirds applied, everything.
The only thing you could see on the photo was a skateboarder dropping in from the coping of a halfpipe. An extreme sport photographer would have made it clear that the drop was around 4 meters high, and would have zoomed out, or used an fish eye to put the whole scene in perspective.
Remember it’s not only about the person itself, it is also its surrounding that can make or break a photo.
Below an example of photo that is great but just has the wrong crop and below the right crop, where you can see the ‘extreme’ part of what the skateboarder is doing, a pretty high wall ride.