Most organized sports award some kind of recognition to the top athlete or team within the sport over some time period. The form these awards take varies from sport to sport. Amateur sports tend to use medals (like those awarded at the Olympics); professional sports often award trophies, but I've also seen individual rings and other similar items.
All of the professional "combat" sports, i.e. boxing, MMA, and wrestling, have always recognized their title holders with a belt: a strap that can be worn around the waist, but which contains an over-sized and highly decorative "buckle" on the front. This form of award is so common that not using it always appears to be a cheap gimmick.
Is there any historical reason why belts are so universal in such sports, but relatively rare elsewhere? I can only find one case where a non-combat sport used a belt -- a single NASCAR race in Vegas awards a belt instead of a trophy, but even that appears to be a gimmick based on the fact that Vegas is famous for boxing, which awards belts.