Former Australian prime minister Tony Abbott claims he was head-butted by a gay rights advocate while walking in the street.
Mr Abbott, who decided two years ago that the people should vote on whether same-sex marriage should be legalised, said he sustained a swollen lip in the attack in Hobart.
He said he was walking to his hotel after attending an anti-gay marriage luncheon when the incident occurred.
The altercation is one of several allegations of violence and vote-rigging that have marred a current postal ballot on whether Australia should lift its prohibition on gay marriage.
Australia and Ireland are the only countries to put the divisive issue to the public to decide.
Mr Abbott remains a government politician and is a vocal advocate for the "no" vote.
The two-month voting process began last week.
"A fellow sung out at me, ’Hey Tony’. I turned around. There was a chap wearing a ’vote yes’ badge," Mr Abbott told Radio 3AW.
"He says: ’I want to shake your hand’. I went over to shake his hand then he head-butted me," Mr Abbott added.
A member Mr Abbott’s staff tussled with the man before he ran off, Mr Abbott said.
"It’s just a reminder of how ugly this debate is getting," he added.
Mr Abbott was prime minister in 2015 when he committed his conservative government to holding a compulsory vote by all adult Australians to decide whether gay marriage should be legal.
He was replaced weeks later by prime minister Malcolm Turnbull, who supports gay marriage.
Mr Turnbull opposed the public vote but agreed to maintain Mr Abbott’s policy in a deal with the government power-brokers who ousted Mr Abbott in an internal leadership ballot.
The Senate refused to fund a compulsory vote, so the government is proceeding with a voluntary postal ballot which critics say is unlikely to provide an accurate picture of public opinion.
Politicians would still have to pass a law to allow gay marriage and several have said they would not allow it regardless of public opinion.