Step 1: What is a Sport Quad?
The first category is sport-utility/beginner. I would have to say this is the smallest category. If you are just starting quadding, this is where to look. These quads do not have clutches, and can have 4WD. Engine sizes range from 229cc (Honda TRX250X) to 421cc (Yamaha Wolverine). Some of these quads have automatic transmissions, while some are semi-auto. Sport-utility/beginner quads are best used in the woods on mild to moderate trail conditions. They can be ridden in the woods very slow to about 3/4 of top speed.
Next is woods-built quads. This is the best category if you are on a beginner quad and want to move up to something better-suited for the woods. These sport quads are anywhere from 282cc to upwards of 600. They never have 4WD and almost always have a solid rear axle. They have manual clutches and are well-suited for popping over logs and going up rocky inclines. Examples are: Honda TRX300X, 400X, and 700XX, Yamaha YZF450X, KTM 450XC ATV and 525XC ATV. These quads can also race, but are beter on the trails. They go on trails from mild to intermediate/advance <450cc, and mild to extreme 450>.
The third and final category is racing quads. They always have clutches and are the most expensive type of sport quad to buy. They need to be ridden fast in the woods or else they can easily stall. Most quad manufacturers only make one race quad. Any quad with the designation "R", "RACE", "Race", is a racing quad. They are almost always 450cc.To ride these in the woods you need to go fast in the woods, and make modifications, most importantly a taller sprocket. This will decrease top speed, but it will help your quad from stalling out when your revs aren't high enough. You may also want to opt for better tires, or even a lift kit, since some are so low to the ground. These quads can be ridden on mild to just short of extreme.