The St Kilda star, 60, argued the woman lied about the incident but Bendigo Magistrate Trieu Huynh on Friday found she was being truthful and convicted him of three charges.
The woman, who cannot be identified, alleged Winmar attacked her at Cohuna in northern Victoria on May 14, 2025.
She claimed Winmar became unexpectedly angry before he grabbed her arm, twisted it and then dragged her by the hair.
The woman also accused Winmar of pushing her against a wall, spitting and yelling in her face, and then bashing her head repeatedly into a wooden door.
The woman said she managed to break free and lock herself into a room, where she called triple zero.
"I was petrified he was going to do more things to me," the woman said in her evidence in May.
"I was actually fearful for my life."
The triple-zero call was played to the court alongside body-worn camera footage from a police officer who attended the scene.
A photo of the woman's arm was also shown, depicting bruising above her right elbow.
Under questioning from Winmar's barrister Dermot Dann KC, the woman accepted she did not tell the triple-zero call taker or the first responding officer what exactly happened.
She admitted she did not disclose the allegations Winmar had dragged her or that he spat in her face but maintained she was telling the truth.
In a recorded chat with a police officer at the scene, Winmar admitted he slapped the woman's arm above the elbow but denied throwing any punches or making her tumble.
He claimed she was the one who punched him five or six times to the face area.
Mr Huynh on Friday found the woman was a credible and truthful witness who was honest in her evidence about the attack.
He accepted there were some inconsistencies in her account but said she had given plausible reasons for those discrepancies.
The magistrate convicted Winmar of two charges of common law assault and one count of unlawful assault, finding the prosecution had proven those offences beyond reasonable doubt.
The charges related to the allegations Winmar grabbed the woman by the arm, dragged her by the hair and hit her head against a door.
Winmar was acquitted on the fourth charge of intentionally causing injury, with Mr Huynh finding the woman's "substantial pain" fell short of the sort of injury required for the charge.
Winmar, who appeared in the Bendigo court in person, dropped his head into his hands after the magistrate handed down his decision.
Mr Dann told the court they would need some time before the pre-sentence hearing to obtain reports in relation to Winmar's rehabilitation.
The defence were also seeking that Winmar be assessed for a community corrections order, Mr Dann said.
The magistrate allowed the longer delay, adjourning the pre-sentencing hearing to August.
Winmar's bail was extended to his next court date in Bendigo.
The 60-year-old was the first Aboriginal footballer to play 200 games in the AFL, finishing his career with 230 games at St Kilda and 21 for the Western Bulldogs.
He fought back against racism in his career, including standing in front of an abusive Collingwood crowd in 1993, lifting his jumper and proudly pointing at his skin.
Winmar is also co-leading a landmark racism class action against the AFL in the Victorian Supreme Court.
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