Girls Aloud singer Cheryl Tweedy cried in court as she explained she only punched a nightclub worker because she was scared of what she might do to her.
Girls Aloud were at number one at the time of the incident
The 20-year-old said Sophie Amogbokpa, a toilet attendant, threw the first punch in the row at the Drink nightclub in Guildford.
She said she felt "scared, angry and upset" after being hit in the face by the 39-year-old and admitted she "whacked" her back.
The singer also admitted swearing at Mrs Amogbokpa, but denied having used any racist abuse against her.
Miss Tweedy, from Heaton in Newcastle, has denied assaulting Mrs Amogbokpa in the incident in the club on 11 January.
Kingston Crown Court had been told the singer hit the toilet attendant after trying to take some lollipops without paying.
But on Wednesday Miss Tweedy told the court she had been reaching into her bag for money to pay for the lollipops when Mrs Amogbokpa hit her on the right side of her face.
She said she was "stunned" by the punch and shouted to her bandmate Nicola Roberts, who she was out with, to get the club's manager.
'A scary woman'
The singer said she felt "scared, upset and angry" and worried about what was going to happen next.
She said "She was a big woman, she was a scary woman, she has got quite broad shoulders."
She cried in the witness box as she admitted to the jury that she had "whacked her back".
Miss Tweedy admitted she had sworn at the toilet attendant and called her names, including "you stupid bitch".
But asked if she had referred to Mrs Amogbokpa as a "black bitch", the pop star said "no".
She told the court: "There's no way, no matter what state I am in, I would refer to anybody by their colour."
Face was hurting
Miss Tweedy, whose band were at number one with their debut single, told the court her new-found fame was "hard work" and meant she could not go out very often.
She went on to say that when she was arrested after the incident she was "confused and frightened".
She told the court her face was hurting and asked to be checked by a doctor as she was due to appear on television the following day.
The singer added that when she was having make-up applied before the programme, she noticed a mark on her face "where I was struck in the face".
Miss Tweedy denies racially aggravated assault occasioning actual bodily harm and an alternative charge of assault occasioning actual bodily harm.
The case continues.