LOS ANGELES >> The California Highway Patrol said Friday it is investigating video of one of its officers straddling a woman and punching her in the head as she lay on the shoulder of a Los Angeles freeway.

The woman had been walking on Interstate 10 west of downtown Los Angeles, endangering herself and people in traffic, and the officer was trying to restrain her, CHP Assistant Chief Chris O’Quinn said at a news conference.

Passing Driver David Diaz recorded the Tuesday incident and provided it to media outlets including The Associated Press.

The officer is on administrative leave while the patrol investigates. He has not been identified.

O’Quinn said the incident report listed no injuries for the woman, who would not give her name. She is undergoing psychiatric evaluation, he said.

He said the officer was answering a report of a pedestrian on the freeway. When he found the woman, she started walking down an off-ramp and then turned around, walked back onto the freeway and started wandering into lanes, O’Quinn said. That’s when the incident occurred.

O’Quinn said the video “only shows a small part of what transpired.”

Diaz, a Los Angeles native who now lives in West LA, told the AP in a phone interview Friday that he arrived when the woman was walking off the freeway. He said she turned around only after the officer shouted something to her.

“He agitated the situation more than helped it,” said Diaz, who started filming soon after.

When the video begins, the officer already is on top of the woman and delivering blows. She can be seen wriggling and trying to sit up.

A man in plain clothes — later identified by O’Quinn as an off-duty law enforcement officer — then appears and helps the officer handcuff the woman.

The video caught the attention of local civil rights leaders, who expressed shock and outrage at their own news conference.

“Speaking for the women of this community, we are angry, we are upset,” said Lita Herron of the Youth Advocacy Coalition.

O’Quinn said he could not say what prompted the officer to act as he did. But he noted California Highway Patrol officers have a heightened sense of the dangers of being on the freeway compared with a citizen “who is not accustomed to the speed and conditions,” especially outside of a car.

“The most dangerous thing that we face is traffic,” O’Quinn said.

He added the CHP would answer community concerns, and that an investigative team already has been assembled and has begun its work.

“We are known as an agency that really polices itself,” O’Quinn said.

Community activist Earl Ofari Hutchinson, speaking at the local leaders’ news conference, agreed.

“Over the years, CHP has had a very good track record in terms of community relations,” Hutchinson said. “That’s why this was so shocking.”

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Associated Press photographer Reed Saxon contributed to this report.