Worried about China's image abroad, Beijing police warned fans attending Sunday's friendly between Barcelona and Beijing Guoan that they would detain those who swore.
Police were positioned in the stands looking for evidence of swearing, fighting or throwing trash, but no fans were reported to be arrested at the game.
"It is just way out of line to have 30,000 people shouting and swearing en masse," police spokesman Liu Chunjiang was quoted as saying. "What we are trying to do is to give the right guidance in how to view a soccer match, not to impose anything on the spectators."
The police used Sunday's match, which attracted 30,000 fans at the 40,000-seat Fengtai Stadium, as a "drill for next year's Olympics," Liu added. The Chinese government is worried that swearing and other "uncultured" behavior like spitting in public and pushing will embarrass the country at the 2008 Olympics, and has been running campaigns to get people to be more "civilized."
The Beijing crowd watched Barca win, 3-0, on goals by Mexican teenager Giovanni Dos Santos, Andres Iniesta and Ronaldinho. Fans paid as much as 1,808 yuan ($235) or a month's salary for many Beijingers to watch the game.
The game was Barca's first on a three-game tour of Asia. It plays Yokohama F-Marinos in Japan on Tuesday and a Mission Hills XI in Hong Kong on Friday.