A police officer "repeatedly punched" a shoplifter who was holding her child, a court heard.
Sisters Pearl, 34, and Wanda Lee, 37, and their mother Emily Smith, 57, were chased by police into The Nelson pub, Norwich, after Asda reported them for stealing £427 of groceries.
Wanda Lee said an officer punched her sister three times while she had her niece in her lap.
All three women were found guilty of or pleaded guilty to theft from a shop.
After the trial at Norwich Magistrates' Court, Pearl Lee said she was considering further action against the police "brutality".
She claimed the attack had left her daughter fearful and wetting the bed.
Wanda Lee, of Swanton Road, Norwich, who had admitted theft but denied obstructing and resisting a constable in his duty, accused Norfolk Police of "racism against gypsies".
A force spokeswoman said the matter was referred to the Professional Standards Department last year and no officers were suspended.
CCTV footage from the pub in Nelson Street captured police officers attempting to arrest the women last March.
Prosecutor Mark Jackson described the four officers involved as handling the women "very robustly".
In a statement read to the court, PC Callum Watson described Wanda Lee as aggressive and "grunting and gnashing" over attempts to be handcuffed.
But Simon Nicholls, defending her, said she had only resisted after seeing the attack on her sister.
'Shouting and screaming'
The CCTV footage showed Pearl Lee on a seat with her toddler on her lap in what appears to be a slapping exchange with PC Peter Forbes-Scott.
It later appears to shows the officer's arm swinging back and forth in a repeated punching-like motion where Pearl was sitting but can no longer be seen.
Cross-examined by Mr Jackson, the officer said she had vented a "tirade of abuse towards me".
"She was shouting and screaming and trying to pull away," he told the court.
Asked if he had manhandled her disproportionately, PC Forbes-Scott said: "I disagree. I think it was entirely in keeping with the situation."
Pearl Lee and Emily Smith, of Swanton Road, Norwich, were each fined £375.
Wanda Lee, who also pleaded guilty to theft and common assault, was fined £355 and given a six-month conditional discharge.