The specifications he recommended for beach volleyball competitions have been in place for 20 years now. Organizers at F.I.V.B. tour events are required to send a sample of the sand that they are considering using — 1 kilogram (2.2 pounds) from layers down to 40 centimeters (about 16 inches).

Since nearly half of the F.I.V.B. tour events take place nowhere near a natural beach but in temporary arenas in places like downtown plazas or city parks, organizers must ship in sand from elsewhere. Knapton makes sure they get the right stuff.

At the 2012 London Olympics, beach volleyball was held at Horse Guards Parade near 10 Downing Street. That sand came from a quarry in Surrey. At the 2008 Beijing Games, all 17,000 tons of the sand came from Hainan Island in the South China Sea. And for the 2004 Athens Games, the world-class beaches of Greece were too pebbly for world-class volleyball. The sand came from a quarry in Belgium.

(Just how finicky are people who want exactly the right kind of sand? Knapton and Hutcheson have filled many golf-course sand traps in the United Arab Emirates with sand shipped from Ontario.)

As with Australia’s Bondi Beach, site of the beach volleyball competition at the 2000 Sydney Games, Knapton and Olympics organizers decided that Copacabana’s sand was good enough. Bringing sand from somewhere else would have violated Brazil’s environmental laws, anyway. They were allowed only to move sand from elsewhere on Copacabana to flatten and build up what is normally a gently sloping beach.

Back in 1987, the first major F.I.V.B. beach volleyball tournament was held on neighboring Ipanema. In 1993, a year after beach volleyball was a demonstration sport at the Olympics, the F.I.V.B. world championships were held on Copacabana. Leaders of the International Olympic Committee were there, and they soon voted to include the sport at the 1996 Summer Games in Atlanta, where it instantly became a popular, television-friendly event that jolted the staid Games with fun and skimpy outfits.