RIO DE JANEIRO — Greg Walker encountered the tallest man in Iran in the dining hall of a hotel in rural China. Walking with crutches, the man, Morteza Mehrzad, ducked beneath a towering archway. Once through, he straightened his back, unfolding his 8-foot-1-inch frame.

Walker’s first thought: Wow.

His second thought: Oh, this is bad.

Walker, who was at a tournament as the head coach of the United States men’s sitting volleyball team, realized Iran had intensified the competition to find tall players leading up to the Paralympics.

A variation of the able-bodied sport, the game is played by people with various impairments who, sitting and sliding along the floor, volley over a nearly 4-foot net.

Height truly matters, and after integrating two players who are 6-foot-7 and 6-foot-10, Brazil emerged as a global power. But with Mehrzad’s entrance into the competition, Walker, and the coaches of other nations, must rethink their strategy. Or find taller players.

“It was as if Iran saw how good a position Brazil’s put themselves in with their height,” Walker said. “Like, ‘OK, we’re going to one-up you. We’re going to pull this guy out of the reserves.’ Great, thanks.”

It is an axiom that holds as true in sitting volleyball as it does in the NFL: When one team develops a successful strategy, others strive to duplicate it.

Iran has taken that charge to the extreme, cultivating Mehrzad over a five-year span to counter Anderson Ribas da Silva, Brazil’s hulking spiker and blocker extraordinaire who played conventional volleyball professionally before knee injuries prevented him from continuing.

The U.S. may find the challenge to catch up fraught. Eric Duda, an American player, said he asked a prosthetist who regularly works with the team to help recruitment by sharing his list of tall clients. Walker has joked with his wife, a clinical medical researcher, about scouring a database for the same.

Or, the U.S. could rely somewhat on happenstance, as Iran did.

The coach, Hadi Rezaei, said he was not actively searching for a player who, when sitting, could look clear over the net. But then one day five years ago he turned on the television.

A program featuring people with physical abnormalities and unusual talents was showing a segment on Mehrzad, and Rezaei, speaking through a translator Saturday night, said he thought, “I could actually use him on my team.”

Rezaei called the network, which helped him contact Mehrzad, who was living in seclusion in a coastal town in northern Iran. Mehrzad, who turns 29 on Saturday, often uses a wheelchair because a bike accident when he was 16 injured his pelvis, causing his right leg to stop growing and be about 6 inches shorter than his left. Embarrassed by his height and a hormonal disorder, acromegaly, that causes changes in facial bone structure, Mehrzad rarely left his home, Rezaei said.

Mehrzad was not made available for interviews Saturday night, after Iran began pool play in the Paralympics by sweeping China, but Rezaei shared details about him.

Before Rezaei found him, Mehrzad had heard of sitting volleyball — after all, the Iranian men had won five gold medals and two silvers across the last seven Paralympics — but had never played before.

“We gave him reason to hope, and he wanted it, of course,” Rezaei said. He added: “I will tell you a key word that he used himself. Before he became famous, when he came out of the house, everybody looked at him very strangely. And then now that he’s famous, when he comes out, everyone wants to take a picture. He became a champion.”

That is what Rezaei told him would happen when he coaxed him into the sport, and at first Mehrzad trained in his hometown, refining basic skills. His progression earned him a spot on the national team in March, when, in his international debut in China, he was selected as the best spiker of the Intercontinental Cup.

“He’s only 50 percent of what he could be at the moment,” said Rezaei, adding that in two years Mehrzad will be “the best player ever.”