The California Highway Patrol (CHP) is investigating footage that shows one of its officers straddling a woman and repeatedly punching her in the head as she lies on the hard shoulder of a Los Angeles highway.
Chris O'Quinn, CHP assistant chief, said on Friday that the woman had been walking on Interstate 10, west of central Los Angeles, endangering herself and people in traffic, and the officer was trying to restrain her.
David Diaz, a passing driver, recorded the incident on Tuesday and provided it to media outlets.
The officer is on administrative leave while the patrol investigates. He has not been named.
O'Quinn said the video only shows a small part of what transpired.
Diaz, a Los Angeles native, told the Associated Press news agency in a phone interview on Friday that he arrived when the woman was walking off the highway. He said she turned around only after the officer shouted something to her.
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.