The violence and arrests that have accompanied Occupy Wall Street protests in several US cities, most notably Oakland, Calif., are raising the question of whether police are becoming too heavy-handed against the movement. Some key incidents:

• In Oakland, where 10,000 marchers shut down the nation’s fifth-largest port Wednesday, violence broke out overnight and 80 protesters were arrested.

• Police officers in Denver used mace and shot paintball-like bullets of pepper spray at protesters in front of the state Capitol Saturday.

• Police in Portland, Ore., arrested 27 protesters who refused to leave a public square Sunday, though no violence was reported.

• On Oct. 11, more than 100 protesters in Boston were arrested after they refused to comply with an order to vacate their encampment.

The contrast between Occupy Wall Street clash incidents and the comparative calm of Occupy camps in places such as Los Angeles makes the protests a useful yardstick for gauging what has worked – and what has not – in crowd control and policing. With protesters calling the movement America's answer to the Arab Spring, academics and police watchdog groups are eager to glean lessons about how US law enforcement can best balance the goals of protecting both free speech as well as law and order.

The report card for Oakland so far is mixed – but perhaps improving.

Some critics have harsh words for the city

“This is a city completely out of control with a police force that doesn’t know which way to turn, a mayor that is indecisive in giving instructions,… all at the mercy of a mob that is fomenting revolution,” says Sam Singer, a political consultant who runs his own public relations firm in neighboring Berkeley, Calif. “This is part of the problem of a leftist progressive mayor who doesn’t want to betray her own political background by taking a hard line when she needs to put an end to this because it is giving Oakland a black eye.”

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But others say the Oakland Police learned volumes from the first episode last week, in which police groups tried to dismantle a downtown encampment.

“I would give them a failing grade of 50 for the first interaction,” says Olis Simmons, executive director of Youth Uprising, an activist group which counsels young people.

She notes, however, that 19 other law enforcement agencies were called in, creating chaos and misunderstanding about standard OPD procedures.

She gives the police an 80 for their behavior during Wednesday's general strike, which brought between 10,000 and 15,000 protesters to the port area for several hours.

“I think they learned from the previous disaster,” she says.

That assessment is echoed by Abel Habtegeorgis, a spokesman for the Ella Baker Center for Human Rights in Oakland. When the police took a surveying role by standing in the background, protests went smoothly and peacefully, with family members of all ages participating. But later, outside agitators arrived to create problems, bringing police into situations that then escalated into violence, he adds.

"Ninety-nine percent of people were perfectly well behaved, and the message was clear until vandals came along and police brought out their tear gas and percussion bombs,” he says. “Then it got ugly.”

In such situations, police are put in a challenging position, says John DeCarlo, former police chief of Branford, Conn., and an authority on police tactics. But their role is one fundamental to American democracy, he says, quoting late sociologist Seymour Martin Lipset: “Born out of revolution, the United States has always considered itself an exceptional country of citizens unified by an allegiance to a common set of ideals, individualism, anti-statism, populism, and egalitarianism.”

Mr. DeCarlo says the police are at the center of this view of American exceptionalism. “It is the hallmark of our system that police must strike the balance between maintaining order in cities and towns while at the same time allowing the First Amendment rights of protesters to speak their message,” he says. “It is a very difficult task to reach the balance between allowing residents to feel safe and yet allow crowds to be free to march and speak.”

Moreover, crowd control forces police to blunt their usual tendencies.

“Ordinarily, cops are trained to take control of the situation: They respond to a domestic violence call, or recent robbery, or homicide scene, by taking over," says Joel Jacobsen, New Mexico's assistant attorney general for its criminal appeals division. "But crowd control is very nearly the opposite. Cops are expected to be passive, to allow things to happen, merely patrolling the perimeter, literally and figuratively."

"So you're asking people not only to do things they're not particularly trained to do, but to behave in a way they're trained not to behave,” he adds.

Yet it can be done. In Los Angeles, arrests have been kept to a minimum, says James Lafferty, executive director of the National Lawyers Guild of Los Angeles, a human rights bar association that facilitates public demonstrations.

“I think it’s a credit to the Los Angeles mayor and city council that they got ahead of this whole movement by discussing ahead of time what it was all about and what they wanted to achieve,” says Mr. Lafferty.

They pre-arranged arrests at a bank sit-in, for example, and the city council passed a resolution allowing the encampment to exist on the city hall lawn, though normal rules prohibit camping. LAPD Chief Charlie Beck has visited the encampment several times and has said publicly that, despite technical infractions, he felt the city should “roll with them because this is an organized national movement.”

Lafferty says he wishes other encampments could learn from the Los Angeles example – especially the lesson of not reacting against peaceful protesters even when agitators are among them. He and his wife were arrested along with other nonparticipants when visiting the New York encampment in Zuccotti Park.

“The Supreme Court has said the police must go after only the agitators,” he says. “Otherwise, it would be a simple matter for someone to shut an entire protest down by just planting a few hooligans. No, you can’t go into these situations wholesale with bean bags and tear gas.”

• Staff writer Gloria Goodale contributed to this report.