In some ways, the activity on a greensward in Southampton, N.Y., last week resembled a regulation polo match. The meaty thwock of a mallet hitting a polo ball punctuated the polite murmur of cultivated sideline conversation as a brightly uniformed player sped toward the goal. But one sound was missing: the thundering hoofbeats of the polo ponies. There was good reason. Instead of riding ponies, the players were astride a variety of bicycles, fiercely competing in a sport that is enjoying a rapid resurgence across the U.S.: bicycle polo.
The rules of bicycle polo are similar to the traditional version, with four...