Sports bags are particularly useful when you are engaged in a sport that requires special gear or when the sport itself requires that the bag have a special feature or two. When purchasing a bag, you should first consider the possible uses of it. Different sports bags are tailored in size and capacity for different sports and different athletes.
When swimming is your sport, for example, it helps to have a bag that can carry all of your swimming gear (which is not difficult since there is not much) AND that is water proof or water resistant to keep your clothes, gear and towel dry. If you play soccer or basketball, you need one that can carry the ball, which is a big ball for both sports. Some have a mesh bag attached to the outside of the main one for carrying the ball. Some bags are large enough to carry the ball inside. If you play field hockey, lacrosse or baseball, you will need a bag that is long enough to carry the sticks or the bat. Tennis bags are typically specifically designed to hold a racket. Some are made to hold two or more racks.
Sports duffles will also provide you with an option for handles. Duffles typically have short handles to be carried with your hands. Sometimes you can find duffle bags with detachable straps for carrying on your shoulder. Some sports bags come as backpacks. Backpacks are easier to use and provide hands free carrying, which can be useful, particularly if you are traveling far or riding a bike. These duffles are designed for multiple uses, each bag is tailor to the sport for which it was made.