A New York Times examination of more than 100 videos from clashes at the University of California, Los Angeles, found that violence ebbed and flowed for nearly five hours, mostly with little or no police intervention. The violence had been instigated by dozens of people who are seen in videos counterprotesting the encampment.

The videos showed counterprotesters attacking students in the pro-Palestinian encampment for several hours, including beating them with sticks, using chemical sprays and launching fireworks as weapons. As of Friday, no arrests had been made in connection with the attack.

To build a timeline of the events that night, The Times analyzed two livestreams, along with social media videos captured by journalists and witnesses.

The melee began when a group of counterprotesters started tearing away metal barriers that had been in place to cordon off pro-Palestinian protesters. Hours earlier, U.C.L.A. officials had declared the encampment illegal.

Security personnel hired by the university are seen in yellow vests standing to the side throughout the incident. A university spokesperson declined to comment on the security staff’s response.

It is not clear how the counterprotest was organized or what allegiances people committing the violence had. The videos show many of the counterprotesters were wearing pro-Israel slogans on their clothing. Some counterprotesters blared music, including Israel’s national anthem, a Hebrew children’s song and “Harbu Darbu,” an Israeli song about the Israel Defense Forces’ campaign in Gaza.

As counterprotesters tossed away metal barricades, one of them was seen trying to strike a person near the encampment, and another threw a piece of wood into it — some of the first signs of violence.

Attacks on the encampment continued for nearly three hours before police arrived.

Counterprotesters shot fireworks toward the encampment at least six times, according to videos analyzed by The Times. One of them went off inside, causing protesters to scream. Another exploded at the edge of the encampment. One was thrown in the direction of a group of protesters who were carrying an injured person out of the encampment.

Some counterprotesters sprayed chemicals both into the encampment and directly at people’s faces.

At times, counterprotesters swarmed individuals — sometimes a group descended on a single person. They could be seen punching, kicking and attacking people with makeshift weapons, including sticks, traffic cones and wooden boards.

In one video, protesters sheltering inside the encampment can be heard yelling, “Do not engage! Hold the line!”

In some instances, protesters in the encampment are seen fighting back, using chemical spray on counterprotesters trying to tear down barricades or swiping at them with sticks.

Except for a brief attempt to capture a loudspeaker used by counterprotesters, and water bottles being tossed out of the encampment, none of the videos analyzed by The Times show any clear instance of encampment protesters initiating confrontations with counterprotesters beyond defending the barricades.

Shortly before 1 a.m. — more than two hours after the violence erupted — a spokesperson with the mayor’s office posted a statement that said U.C.L.A officials had called the Los Angeles Police Department for help and they were responding “immediately.”

Officers from a separate law enforcement agency — the California Highway Patrol — began assembling nearby, at about 1:45 a.m. Riot police with the L.A.P.D. joined them a few minutes later. Counterprotesters applauded their arrival, chanting “U.S.A., U.S.A., U.S.A.!”

Just four minutes after the officers arrived, counterprotesters attacked a man standing dozens of feet from the officers.

Twenty minutes after police arrive, a video shows a counterprotester spraying a chemical toward the encampment during a scuffle over a metal barricade. Another counterprotester can be seen punching someone in the head near the encampment after swinging a plank at barricades.

Fifteen minutes later, while those in the encampment chanted “Free, free Palestine,” counterprotesters organized a rush toward the barricades. During the rush, a counterprotester pulls away a metal barricade from a woman, yelling “You stand no chance, old lady.”

Throughout the intermittent violence, officers were captured on video standing about 300 feet away from the area for roughly an hour, without stepping in.

It was not until 2:42 a.m. that officers began to move toward the encampment, after which counterprotesters dispersed and the night’s violence between the two camps mostly subsided.

The L.A.P.D. and the California Highway Patrol did not answer questions from The Times about their responses on Tuesday night, deferring to U.C.L.A.

While declining to answer specific questions, a university spokesperson provided a statement to The Times from Mary Osako, U.C.L.A.’s vice chancellor of strategic communications: “We are carefully examining our security processes from that night and are grateful to U.C. President Michael Drake for also calling for an investigation. We are grateful that the fire department and medical personnel were on the scene that night.”

L.A.P.D. officers were seen putting on protective gear and walking toward the barricade around 2:50 a.m. They stood in between the encampment and the counterprotest group, and the counterprotesters began dispersing.

While police continued to stand outside the encampment, a video filmed at 3:32 a.m. shows a man who was walking away from the scene being attacked by a counterprotester, then dragged and pummeled by others. An editor at the U.C.L.A. student newspaper, the Daily Bruin, told The Times the man was a journalist at the paper, and that they were walking with other student journalists who had been covering the violence. The editor said she had also been punched and sprayed in the eyes with a chemical.

On Wednesday, U.C.L.A.’s chancellor, Gene Block, issued a statement calling the actions by “instigators” who attacked the encampment unacceptable. A spokesperson for California Gov. Gavin Newsom criticized campus law enforcement’s delayed response and said it demands answers.

Los Angeles Jewish and Muslim organizations also condemned the attacks. Hussam Ayloush, the director of the Greater Los Angeles Area office of the Council on American-Islamic Relations, called on the California attorney general to investigate the lack of police response. The Jewish Federation Los Angeles blamed U.C.L.A. officials for creating an unsafe environment over months and said the officials had “been systemically slow to respond when law enforcement is desperately needed.”

Fifteen people were reportedly injured in the attack, according to a letter sent by the president of the University of California system to the board of regents.

The night after the attack began, law enforcement warned pro-Palestinian demonstrators to leave the encampment or be arrested. By early Thursday morning, police had dismantled the encampment and arrested more than 200 people from the encampment.