(07-16) 06:50 PDT OAKLAND -- Protesters outraged at the acquittal of George Zimmerman in Florida briefly blocked a freeway in downtown Oakland and tried to get on a second freeway Monday night in the city's third demonstration in as many days.

Dozens of protesters walked onto northbound Interstate 880 at Broadway about 7:15 p.m., shortly after marching past Oakland police headquarters. Officers led at least one protester in handcuffs off the freeway.

Police removed demonstrators within 15 minutes, and the protesters continued marching downtown, at times blocking motorists and spray-painting graffiti on buildings, before continuing near Lake Merritt and trying at about 8:45 p.m. to get onto eastbound I-580, where they were met by police in a skirmish line. They headed back around the lake, but not before some people set off illegal fireworks and burned an American flag.

The crowd eventually headed back to 15th Street and Broadway, and at 10:45 p.m. people smashed windows of a Comerica bank, a Men's Wearhouse store and a vacant retail space. Police rushed in to make arrests, which led to skirmishes between protesters and police. During the chaos, a tear-gas canister was detonated, and officers were the target of rocks and bottles.

As the night wore on, violence grew. About 11 p.m., a masked protester hit a waiter at Flora Restaurant and Bar on Telegraph Avenue in the face with a hammer as he tried to protect the restaurant, whose windows were broken two nights ago.

By night's end, police had arrested six men, two women and a male juvenile, with most of them hailing from outside Oakland, said Officer Johnna Watson, a department spokeswoman. The offenses included assault with a deadly weapon, resisting arrest and vandalism.

It was the third protest of the Zimmerman verdict in the city since Saturday night. In moving quickly, police avoided a repeat of a 2010 rally in which 150 people protesting education budget cuts were arrested for walking onto the same stretch of freeway and shutting it down for an hour.

Merchants clean up

Earlier Monday, Natalie Nadimi smiled politely as an Oakland city official told her that public works crews were boarding up broken windows and picking up debris for free at businesses damaged over the weekend.

Nadimi is the community engagement manager at Oaklandish, a retail shop on Broadway whose clothing celebrates the city. The store had already boarded up two of the four windows smashed Saturday night, and Nadimi had a different concern.

"There weren't really any police out," she said. "Do you know why there weren't any police?"

Juno Thomas, the city's business development coordinator, said police had been downtown that night but also apologized. He said the force was "spread kind of thin" and that officers would be ready for any additional protests "to prevent further damage."

It was one of many stops Thomas made Monday as downtown merchants went through a familiar ritual - picking up the pieces from back-to-back weekend protests, much as they did after Occupy Oakland rallies in 2011 and a series of demonstrations related to the killing of unarmed BART rider Oscar Grant in 2009.

On Saturday night, masked vandals within a crowd of about 150 people started fires, smashed windows of shops and restaurants, slashed car tires, damaged a BART police car and spray-painted "Kill Zimmerman" and antipolice epithets on the Alameda County courthouse and other locations.

At Dogwood, a bar at 17th Street and Telegraph Avenue, some patrons were cut by shattered glass, the owner said. But police made no arrests Saturday night.

Quan blasts vandalism

On Sunday night, several hundred protesters marched through the streets. There were minor reports of vandalism, and police made one arrest. Several journalists, however, including photographers for The San Francisco Chronicle and the Bay Area News Group, were accosted by protesters late in the night near Dogwood, suffering minor injuries.

The vandalism left merchants frustrated. Some said they agreed with protesters that Zimmerman's killing of Trayvon Martin, an unarmed African American teenager, was a tragedy that highlighted racial injustice. But they wondered why people angry at the acquittal would damage local businesses.

Many peaceful protesters were also upset, saying the vandals represented a small percentage of demonstrators and seemed to be focused more on causing damage than fighting for justice.

After its windows were broken Saturday, Dogwood put up a poster with Martin's picture that read, "I am Trayvon Martin and my life matters." At Awaken Cafe on Broadway, owner Cortt Dunlap put a sign over a damaged window reading, "This window will be fixed later today. When will the U.S. Justice System?"

"I think when a local business culture thrives in a community," Dunlap said, "a lot of the social-justice issues that we see in the Trayvon Martin and George Zimmerman case start to go away."

Oakland Mayor Jean Quan agreed, saying Monday that the damage "gives us a bad image."

"When you break the windows of restaurants, you're really hurting the economy, and you're hurting the jobs that are being created in the city," Quan said.

Interim Police Chief Sean Whent said Monday that the department didn't realize that deliberations in the Zimmerman case would take place Saturday and didn't expect a verdict "would come in that quickly."

Whent said 50 officers were brought in from throughout the city to augment the eight to 10 officers downtown, and with the limited staffing, it would have been unwise for officers to wade in to arrest vandals in "that kind of crowd."