The video posted on YouTube shows the cop pursuing the woman on foot past an I-10 on-ramp. Those recording it can be heard laughing at first. (Warning: video contains NSFW language).
But the laughs quickly subside as the cop grabs the woman, who is either pulled down or falls to the ground, and then repeatedly punches her.
CHP says the officer asked the woman to stop, but she refused and continued to walk away from him.
"A physical altercation ensued as the pedestrian continued to resist arrest, at which point a plain clothes, off duty officer assisted in applying the handcuffs," the CHP said in a statement given to KABC.
The woman refused to give her name and is identified only as "Jane Doe." KABC says she was taken to a hospital for physical and mental evaluation.