Stephen Jolly faced Melbourne Magistrates Court on Monday when he pleaded not guilty to one charge of assault.
The City of Yarra mayor, whose inner-city council covers Richmond and Collingwood, is accused of assaulting Estella Burrows after she and two other masked intruders gatecrashed Jolly's post-election party in Fitzroy on November 1, 2024.
A four-day contested hearing into the matter was told at least 14 witnesses and medical professionals will be called to give evidence.
Prosecutor Laura Zubrecky told the court the trio arrived at the event, one holding a megaphone and another with a banner, before chanting and being asked to leave.
One member was heard on a video posted to social media calling Jolly a "prolific domestic abuser".
"The accused approached the group and the prosecution alleged that the accused punched (Ms) Burrows with his right hand, hitting her in the left side," Ms Zubrecky said.
"The group was escorted out of the venue soon after."
Defence lawyer Michael McGrath told the court the evidence would not establish beyond a reasonable doubt that Jolly had assaulted the victim.
If the court found his client did make contact, it was in self-defence during a "rapidly developing scuffle", Mr McGrath said.
Jolly, who remains mayor of the inner-city council, reported the group's attendance to police later that night.
Ms Burrows formally reported the alleged assault to police 10 months later.
Testifying on Monday, she said the trio went to the gathering with intentions to protest peacefully, aiming to draw attention to the re-election of Jolly and his alleged history of violence and ill-treatment of women.
They brought masks, including an Egyptian mummy mask purchased from a supermarket, as they did not wish for their faces to be shared in a video that would be taken and shared online, Ms Burrows said.
Once inside, the activist said she had planned to unfurl a banner while another spoke on the megaphone with a third filming the interaction.
Ms Burrows told the court it was in that moment when Jolly allegedly punched her in the face.
"He moved towards me with extreme haste ... he punched me without hesitation, without warning," she told the court.
"I believe his shirt was untucked, (and he was) filled with rage."
The hearing continues on Tuesday.