A large protest in Brooklyn against Israel’s military offensive in Gaza erupted into a chaotic scene on Saturday, as the police arrested dozens of pro-Palestinian demonstrators and at times confronted them violently.

In videos posted on social media, officers can be seen punching at least three people who were prone on the ground at the demonstration in the Bay Ridge neighborhood. The aggression was corroborated by witnesses. Another protester who was filming the police was tackled and arrested. A police spokesman declined to comment on the officers using force on protesters.

The police said Sunday that 40 people were arrested. They have not released details on the charges the protesters face.

“I saw police indiscriminately grabbing people off the street and the sidewalk,” said Nerdeen Kiswani, founder of Within Our Lifetime, an activist group led by Palestinians that organized the demonstration. “They were grabbing people at random.”

According to the Police Department’s patrol guide, officers must use “only the reasonable force necessary to gain control or custody of a subject.”

In recent years, Within Our Lifetime has put on an annual mid-May rally in Bay Ridge, a neighborhood with a large Arab population, to commemorate what Palestinians call the Nakba, or “catastrophe” — when hundreds of thousands of Palestinians were forced from their homes during the war that led to Israel’s founding in 1948.

Given the war in Gaza and months of protests in New York, this year’s protest was charged from the start. It started at 2 p.m. at the intersection of Fifth and Bay Ridge Avenues. Within about 25 minutes, a large group of officers arrived and warned protesters to get onto the sidewalk. Those who remained in the street would be arrested, the police told them.

From there, the event alternated between protest marches and standoffs with the police. In one video taken by Katie Smith, an independent journalist, a police commander in a white shirt delivers at least three punches to a person lying on the pavement. In another video she recorded, an officer punches a man who is on the ground at least six times and a white-shirted commander aims a kick at the man, though it is not possible to see if it landed.

In a separate instance filmed by another independent journalist, Talia Jane, an officer flings a protester against a signpost and then hurls him to the pavement, where he is pinned by two officers as he is punched by a third.

The footage of the police, including at least one commander, pummeling protesters recalled some of the N.Y.P.D. conduct caught on video at the Black Lives Matter demonstrations in 2020. The city ended up paying $13 million to settle a class-action suit brought by those protesters.

In a video of the Saturday protest posted on Twitch, half a dozen people could be seen filming a group of police officers and commanders walking on Bay Ridge Avenue. A police commander grabbed the nearest one, followed by two more commanders and a scrum of blue-shirted officers.

The protester was shoved to the ground, handcuffed and arrested. Other people in the crowd continued recording the event.

Those arrested were led to police vans and driven to the headquarters in Manhattan. A light rain began to fall, and by 8 p.m. the protest had dispersed.

Sabir Hasko contributed reporting.