Actor Johnny Depp knelt on ex-wife Amber Heard and hit her on the back of her head during a row about a pre-nuptial agreement, she told a court.
Ms Heard also said she had "very little decision-making power" in the marriage.
Mr Depp, 57, is suing the publisher of the Sun over an article that referred to him as a "wife beater" - but the newspaper maintains it was accurate.
He denies 14 allegations of domestic violence on which News Group Newspapers is relying for its defence.
Taking to the witness stand at London's High Court on the 10th day of the case, Ms Heard said she had been subjected to repeated and regular physical violence by the time of the couple's marriage in 2015.
She was asked about allegations of an argument in January 2015 over discussions with lawyers about a pre-nuptial agreement between herself and Mr Depp.
"There was an argument in a hotel room in Tokyo that resulted in Johnny kneeling on my back and hitting me on the back of the head," Ms Heard told the court.
She added: "But then Johnny was also accusing me of having an affair with a co-star and that is what led to the actual argument."
The actress was also asked by Mr Depp's lawyer, Eleanor Laws QC, whether she had had "ultimate control in the relationship". Ms Heard replied: "No, absolutely not."
Asked whether she took important decisions in the relationship, Ms Heard said: "No, I had very little decision-making power in that relationship."
She was asked about five penthouse apartments in the Eastern Columbia Building in Los Angeles, which her sister and friend moved into.
Asked whether they paid any rent, Ms Heard said: "No, Johnny wouldn't let them."