The undercover cop who pulled a gun on anti-police protesters in Oakland, California, was justified in doing so after a gang of 50 targeted his partner, a witness claims.
The officer, who has not been named, was marching with the demonstrators on Wednesday night when the mob is said to have turned on him and his colleague.
After pulling out a baton and identifying himself as police, his partner was hit on the head and tackled to the ground - prompting the officer to point a pistol at the crowd.
Despite a flurry of outrage from crowds and on Twitter, photographer Michael Short said the reaction was natural in the face of the 'threatening' crowds.
Undercover: This (center, in brown) is the undercover cop marching with anti-police protesters and his partner (right, in the green cap) moments before the mob of 50 turned on them and hit his partner in the head
Turned on them: The crowds started shouting 'they're cops!' and advanced on the officers, witnesses said
Reaction: After being hit on the head and tackled, the officer's partner slammed a protester to the ground
Pulled his gun: The officer then pointed his gun at the protesters in a move that has sparked outrage
Short, 38, who freelances for the San Francisco Chronicle, told NBC News: 'It was an appropriate response.
'I would have been scared if I saw my partner get knocked to the ground.
'He was justified. I felt threatened by the protesters, too.'
KTVU reported that demonstrators screamed at the undercover officers during the march 'Hey, they're undercover, they're cops!'
The officers' faces were masked at the time, the affiliate station reported.
10 For thy violence against thy brother Jacob shame shall cover thee, and thou shalt be cut off for ever.
40 And by thy sword shalt thou live, and shalt serve thy brother; and it shall come to pass when thou shalt have the dominion, that thou shalt break his yoke from off thy neck.