Ryan Giggs "deliberately headbutted" ex-girlfriend Kate Greville during an altercation in November 2020, a prosecutor told Manchester Minshull Street Crown Court on Monday.
Giggs, who played for Manchester United and recently coached the Wales national team, faces charges of controlling and coercive behaviour, and assault, stemming from alleged abuse of Greville from 2017 until 2020.
The 48-year-old appeared in court for the case's opening day and has denied all charges.
What allegations were made against Giggs?
Prosecutor Peter Wright QC said in court that during a November 2020 incident, Giggs "entirely lost self-control and he deliberately headbutted [Greville], thereby causing swelling to her lips and bruising".
Wright said that was just one instance of abuse over a three-year period, and that Giggs exhibited a pattern of "sinister" behaviour.
Other allegations included a claim that Giggs intentionally elbowed Greville's sister, Emma, and was regularly emotionally abusive towards his then-girlfriend.
Through defence lawyer Chris Daw QC, Giggs denied all charges.
"There were lines Mr. Giggs would never cross," Daw told jurors.
The trial is expected to last about 10 days and will relocate to Manchester Crown Court on Tuesday.
Giggs' Wales resignation
Wales suspended the head coach in 2020, and he quit his post in June. Rob Page has stepped up in Giggs' absence to lead the nation to a first World Cup appearance since 1958.
"It is only right that the Wales FA, the coaching staff and the players prepare for the [World Cup] tournament with certainty, clarification and without speculation around the position of their head coach," Giggs said in a statement announcing his resignation.