After a planned speech in February by the right-wing writer Milo Yiannopoulos attracted demonstrators who started fires and shattered windows, the University of California, Berkeley realized it had a major hole in its event planning.

“We did not have enough police officers,” said Dan Mogulof, assistant vice chancellor for public affairs at Berkeley.

So beginning this semester, student groups hosting large events are required to inform the college at least eight weeks in advance, so it has time to prepare a security plan. For the most controversial speakers, hundreds of police officers will be drawn from across the University of California system and also, under mutual aid agreements, from municipal police departments across the region. Security checkpoints and buffer zones will be erected around venues.

Berkeley is ready to spend as much as $500,000 to protect a single lecture, Mogulof said, and will do so regardless of the speaker’s ideology.

The new protocol was unveiled on Sunday, a day after a woman was killed and dozens of people were injured in Charlottesville, Virginia, after a series of white supremacist gatherings at the University of Virginia and in the city. The timing was a coincidence, but across the country, college administrators and law enforcement officials are bracing for a wild fall of protests as their campuses become battlegrounds for society’s violent fringes.

On Aug. 14, Texas A&M University announced that it would cancel a planned Sept. 11 appearance by the white nationalist Richard B. Spencer, who was billed as a lead speaker of the “Unite the Right” rally in Charlottesville. After an appearance by Spencer in December, Texas A&M changed its events policy to require that all speakers be invited by a student group, one of several rules colleges are enforcing as a way to control who appears on campus. Still, the person who invited Spencer to Texas A&M, a man who briefly attended the school years ago, said he would pursue legal action on free speech grounds.

At the University of Florida, the events policy allows outside groups to rent space, even without student partners. Nevertheless, today the school announced it had denied Spencer’s request to appear there on Sept. 12. It cited the violence in Charlottesville and social media posts declaring, “The Next Battlefield is in Florida.”

Kent Fuchs, the university’s president, said in a statement, “The likelihood of violence and potential injury — not the words or ideas — has caused us to take this action.”

It is unclear if such an explanation would hold up in court, should Spencer challenge it. Indeed, Spencer’s movement presents a host of legal and logistical challenges for university administrators.

Because of the First Amendment, colleges and universities that rely on public funding have few legal options in preventing offensive lectures from taking place, especially if a student group is affiliated with the event.

In April, a federal judge ruled that Auburn University, a public institution in Alabama, could not block an appearance by Spencer, because the university had not demonstrated a specific threat of imminent violence. Hundreds of people protested the speech, resulting in skirmishes and three arrests.

Even the violence in Charlottesville is not likely to help universities make a case in court. “Unless the group lays out an intention that they’re going to do something dangerous or violent, you’re stuck with letting them have their meeting,” said Tony Buzbee, a Houston lawyer and a regent for the Texas A&M system.

The First Amendment safeguard is a major reason that colleges, especially public ones, have become a favored forum for right-leaning speakers, from mainstream conservatives to racial provocateurs of the so-called alt-right, a movement that embraces white nationalism. Another reason is the colleges’ reputations as breeding grounds of left-wing ideology, virtually guaranteeing protests and news media attention.

At a news conference at his Alexandria, Virginia, office on Aug. 14, Spencer said he chose to speak on campuses because they “have become the absolute bastion of the left.” He added, “It’s great to go to the belly of the beast.”

Until recently, most colleges’ protest protocols were suited to the relatively peaceful student activism of the 1990s and early 2000s. Demonstrations over apartheid, abortion rights or sexual assault rarely became violent; students marched and shouted, and then went home safely at the end of the day.

But that was before the flowering of the alt-right and the response by militant left-wing anti-fascist groups, as well as the ease with which social media makes it possible to draw outside demonstrators to a campus.

“We’ve now entered an arena where the controversial speakers are not only bringing out forms of hatred, but also forms of violence,” said Sue Riseling, the executive director of the International Association of Campus Law Enforcement Administrators and the former chief of police at the University of Wisconsin, Madison. Proper preparation today, Riseling said, should include a plan to physically separate opposing groups with a history of violent confrontation, as well as coordination with local, county and state police forces.

Her organization plans to host trainings across the country in October, to help campus police forces prepare for unrest.

Next month, Berkeley is expecting several conservative speakers who have a history of attracting impassioned protest. The College Republicans and the Young America’s Foundation will host the writer Ben Shapiro. The California Patriot, a student magazine, plans to host Yiannopoulos as part of a four-day free-speech event, and has also extended invitations to Ann Coulter and David Horowitz, both of whom were scheduled to speak at Berkeley in the spring, only to see their events canceled amid safety concerns.

Naweed Tahmas, a Berkeley senior and external vice president of the Berkeley College Republicans, said he was concerned that the university’s new events policy allowed administrators to impose curfews or other limitations that would effectively prevent conservatives from speaking. Some colleges have required speakers to appear in the middle of the day, since nighttime events tend to draw more demonstrators and can be harder to control. The dates and times were points of contention when the appearances by Coulter and Horowitz were called off.

Richard Cohen, the president of the Southern Poverty Law Center, a nonprofit that tracks hate groups, said colleges would be wise to not block extremists from appearing.

“We might want to shame them, or think they are sick, but students have a right to listen to who they want to listen to, and we don’t have the right to censor that,” he said.

He also pleaded, perhaps optimistically, that protesters refrain from shouting down or attacking white supremacists, so they would be denied the opportunity to portray themselves as free speech martyrs.

“Don’t give these fools an audience,” he said.