A chunk of concrete fell from the underside of RFK Stadium's upper deck during D.C. United's Major League Soccer game last night, hitting an empty seat 20 feet below and scattering about a dozen spectators. No one was hurt, officials said.

Stadium officials sealed off the area, and the spectators from Section 310 moved elsewhere to watch D.C.'s 3-1 victory over the Miami Fusion. Several softball-sized chunks of concrete remained scattered around several rows of seats as the game continued.

Witnesses' estimates of the size of the concrete chunk varied, with one observer holding his hands about a foot and a half apart. Tony Burnett, stadium manager, said it was about 10 inches in diameter.

"This happens all the time," said Jim Dalrymple, the stadium's general manager, who said slivers of concrete often loosen as the building settles. "We have people going around checking for it all the time."

"It's really nothing," said Burnett, who described the "concrete flake" as weighing less than a pound. "It could have put someone out, I suppose, but it wasn't a big piece. The building is structurally sound."

The crash of the concrete hitting the seats could be heard at least three sections away. "All I heard was a smash that sounded like ice," said fan Mike Testa, of the District. "There was a whole crowd of people sitting there."

Lois Lightfoot, of Springfield, who had been sitting in Row 6 of Section 310, gazed through her binoculars at the hole in the ceiling after moving to another seat. "It was lucky it didn't hit anybody," she said. "We don't normally need to wear helmets when we come here."

Staff writer Allan Lengel contributed to this report.