The Sport ATV category is for the trail rider or racer at heart. Companies like Can-am, Honda, Yamaha, Kawasaki and many more, designed there sport bikes for both the track and the trail. If you like to go fast, switching gears and powering through the holeshot at your local track these are the bikes for you.
Just like the rest of the ATV's there is many different displacements and sizes for each sport ATV. They very from 90cc to the more extreme 450's for the more experience riders. Just like the others if your a beginner at the sport, its not wise to jump on a bigger more aggressive bike. You should start with something smaller and more manageable for your style of riding. Once you feel more confident in your riding ability, your understanding and respect for the more larger, faster ATV's will be a lot easier to ride.
The other major bonus to look into is suspensions setups. This helps for better control, handling around corners and taking impacts of those whoops or jumps at the track or rougher trails you may encounter out in the backwoods. The other things to look at when buying a sport ATV's is accessories and features that can help make your riding style that much more comfortable for you.
Some first hand buying experience for a sport ATV is you want to look for something more nimble around corners. You want to look for something that feels right to you on the trail or track. Just because it might be the fastest on the track doesn't mean your going to have a good handling bike. Suspension and handling is a key factor in any bike, if you don't have those things the faster the bike the harder its going to be able to hold on too. Same on the trails, you want a bike thats average or suites your riding style.