"What we found out was that sports are a very nationalistic thing. Boxing is a one-on-one sport. People like rooting for fighters they can identify from their country."

Arum says Chinese cheered zealously for Zou during his pro debut in Macao in early April.

The rise of such stars has generated more interest in amateur fights.

Green and his competitors underwent arduous two-hour sessions three days a week for three months. It was so intense that steam could be seen swirling off Green's head at one point.

Their preparations include weight training, physical conditioning and boxing techniques.

The culmination of these dozens of hours of punishing drills is a final totaling eight minutes in the ring. Each fight is two minutes, plus a minute or so for strutting and another 30 seconds between rounds.

Training started early summer. Fighters were selected halfway through. The 23 chosen contestants, including accountants, editors, researchers and engineers, joined the Brawl on the Wall event.

On the final night, Green is jumpy and energetic as he awaits his moment in the spotlight.

He seems nervous but insists he isn't. He says he knows he'll do well.

"I'm not going to die," he says.

"I know I've been practicing a lot. This is the reward - putting everything I've learned on the line."

The bell rings. The fight begins.

The crowd roars as punches fly.

Someone shouts: "Sam! Sam! Sam!"

The final bell rings. Green steps out of the ring.

He sees the world a little differently. That's not just because he's missing a contact lens and a shiner is emerging under his right eye. He lost the fight. But he still feels like a winner.

"Worth it! Totally worth it," he says.

"This is like the best experience ever."

Sun Xiaochen contributed to this article.