Fighters were instructed to punch slowly at first, one punch at a time, and then gradually build up to a sequential flurry. Mistakes were rare — such as when a visually impaired participant accidentally hit a volunteer in the face. They were advised beforehand not to punch upward.

"The key for us in boxing is to react quickly, depriving the opponent of time to assess the situation," Deng said. "Otherwise, you could really get killed on the defensive."

After half an hour of practice, a brief match between two visually impaired contestants — without volunteer assistants — was arranged. Everyone got a turn.

"After the practice, the match was particularly exhilarating," Deng said. "My opponent and I leaped into the fray and punched like we were fighting an enemy."

She said her hands and feet were sore afterward.