OS ANGELES - In the first tense confrontation of Democratic National Convention week, police fired pepper spray and rubber bullets at unruly protesters last night, with officers on horseback sweeping through the crowd to force it to disperse.
As protesters and fans attending a free rock concert outside the convention hall struggled to stay on their feet, police who had spent an hour dodging bottles, rocks, and other debris moved in to end the event.
Stuart Maslin, the LAPD captain in charge at the scene, described the sequence of events from the police point of view:
''A dispersal order was given by the stage. They were given 15 minutes to disperse. There were bonfires starting to be lit. We kept warning them, at 5 minute intervals, to disperse. Twenty minutes passed, and something had to be done.''
A police spokesman, Charles Rodriguez, confirmed that police had fired ''skip rounds,'' foam pellets designed to bounce off the ground and hit protesters in the legs. He could not confirm the use of pepper spray or other riot control materials.
In an otherwise peaceful day of protests, the standoff began after 400 police officers in full riot gear surrounded the large fenced-off parking lot where demonstrators are permitted to gather daily. On one side of what has been dubbed the protest pit, calm held, with demonstrators holding hands to form human chains to keep the crowd from surging toward police. But on the other side, a small band of black-clad youths began throwing bottles and other objects at officers.
One young man was pinned against a plastic barricade. Police officers cracked him with a baton and shouted, ''Get out!'' A woman injured her leg. ''The world is watching,'' she said.
A security guard for a radio station and a colleague were atop a one-story building when they were struck by rubber bullets. The guard, who refused to give his name, said he was shot in the leg, back, and left forearm.
He called his wife and said: ''We'll be back tomorrow. We'll probably be shot again.''
His colleague was shot on his left arm and above his left eye.
James Grosso, who works for the city of Los Angeles department of water and power and was parked in his city vehicle, also said police were firing the rubber bullets, which were dispersed from a canister.
Ted Hayes, 49, chairman of the National Homeless Convention, which is also running this week in Los Angeles, said he was struck in the stomach by a rubber bullet and hit his head on a concrete wall as he fell.
Police said 10 people were arrested during last night's confrontation, bringing the total of convention-related arrests to 38. At least four people were injured.
John Quigley, 39, of Venice, who was one of hundreds of protesters, said the group was peacefully dispersing, but then a hundred police officers charged.
''I was in Seattle. I was in Washington D.C. I've seen police department tactics, but there was an abruptness to this situation that was uncalled for,'' Quigley said. ''Suddenly there was indiscriminate shooting of rubber bullets, a burst of shots.''
''Why don't they just walk away and let the people throw bottles at an empty parking lot?'' said Scott Fleming, a lawyer who had volunteered to monitor the demonstration for the National Lawyers Guild, which is providing its services free of charge. ''They could certainly end this situation real quick by walking away. By staying here, they're just making themselves a target.''
But like the protesters and concert-fans who put their faces to the fence, fleeing only when the air grew acrid and then only briefly, police refused to back down.
The incident began shortly after the concert by the protest alternative rock group Rage Against the Machine ended and as another band took the stage. But it went largely unnoticed by the rest of the crowd, which danced and sang.
Shortly before the concert, police on foot, motorcycle, horseback, and bicycle had swamped the area around the Staples Center, hoping both to protect property and prevent trouble.
''I'm here to lend solidarity to the struggle,'' said a 25-year-old college student who would identify herself only as Janice. ''That fence is very provocative. But we can't go away. We can't be quiet. That's what they want and we can't let them win.''
But, as some protesters put it, ''they'' had won. In the weeks leading up to the convention and on its first official day, organizers and activists had fretted again and again that their message would be lost if peace did not hold.
On Sunday, his face pressed against the chain-link fence encircling the protest pit, Jonah Zern had shouted, pleaded, to be taken seriously. In the background, speaker after speaker took to the microphone. Several thousand demonstrators roared their approval. But Zern, a 22-year-old recent college graduate, worried that no one who wasn't nearby would hear.
''We're protesting to protest,'' said Zern, whose T-shirt advertised a group called Students Alliance to Reform Corporations. ''We have to protest. To be heard in the United States, you have to have wealth. For the average person, you have to find another way.''
Above the din, one concern came through loud and clear: Regardless of specific issue, these demonstrators no longer believe that America belongs to Americans. It is what unites them, they say, even when their agendas overlap or conflict.
''What is really boils down to, at least here at the DNC, is that we don't have a say in politics anymore,'' said Meagan Cartwright, a 20-year-old college physics major from Seattle who is an intern at a nonprofit organization working to stop global warming and save the ozone layer. ''That's what brings us all together.''
Walter V. Robinson of the Globe Staff contributed to this report.
