Tasmanian police will investigate Tony Abbott's claim that he was headbutted by a same-sex marriage supporter in Hobart on Thursday after the former prime minister lodged a formal complaint.
Mr Abbott made his complaint to Tasmanian police when they phoned him after learning of the incident via media interviews.
The "no" campaigner said on Friday his office's first action had been to notify the Australian Federal Police.
In a statement, Tasmania Police urged the alleged attacker to turn himself in. They said they contacted the former prime minister after "becoming aware of the claims".
"Police would particularly like to hear from the other man who was allegedly involved in the incident and have urged him to come forward and contact police."
Prime Minister Malcolm Turnbull called Mr Abbott as soon as he heard about the incident and also spoke to the Australian Federal Police Commissioner Andrew Colvin.
Mr Abbott said he was attacked leaving the offices of The Mercury newspaper where he had been meeting with the editor at about 4.35 pm.
"A fellow sung out at me 'Hey, Tony', I turned around, there was a chap wearing a vote 'Yes' badge," he said.
"He says 'I want to shake your hand'. I went over to shake his hand and he headbutted me."
Mr Abbott said while "he wasn't very good at it," the man did make contact and gave Mr Abbott a "very, very slightly swollen lip".
Mr Abbott said his staffer grappled with the man who ran off "swearing his head off."
He said the attack exposed the ugly side of the Yes campaign.
"It was just a reminder of how ugly this debate is getting and the ugliness is not coming from the defenders of marriage as its always been understood," the former prime minister said.
"The ugliness, the intolerance and in this instance, even the hint of violence, is coming from those who tell us in the name of decency, and fair-mindedness and freedom we've got to allow same sex marriage."
"The 'love is love' brigade aren't showing a lot of love I've got to say," he said.
"It was just very disconcerting to find the 'love is love' brigade, or at least someone who was advocating a 'yes' vote, under the guise of wanting to shake your hand in fact try to give you a so-called Liverpool kiss."
Prominent campaigners and MPs on both sides were swift in condemning the alleged attack, including Tasmanian Labor MP Brian Mitchell and Labor MP Stephen Jones.
The assault on Tony Abbott in Hobart cannot be condoned nor justified. It was wrong and criminal and the attacker should be charged.??? Brian Mitchell MP (@BrianMitchellMP) September 21, 2017
Whoever did the Abbott head butt thing... bloody idiot.??? Stephen Jones MP (@StephenJonesMP) September 21, 2017
Liberal senator Eric Abetz, who was sacked from cabinet following Mr Abbott's demise as prime minister, leapt to his colleague's defence.
"Disappointed a yes campaigner would try to assault fmr PM. Must be condemned by all," he wrote on Twitter.
Independent NSW MP Alex Greenwich, who represents the peak lobby group Australian Marriage Equality, warned the attack could harm the 'yes' campaign's plea for voters to endorse marriage equality.
"Anything that distracts from what this reform is truly about is completely an unnecessary distraction," he said.
"This is an act that is not representative at all of the Yes campaign and the respectful campaign which we have been running and continue to run."
And he noted that it was not the first report of violence during the campaign, pointing to the claims made by former prime minister Kevin Rudd who posted a photo of his injured godson saying he had been bashed for supporting same-sex marriage.
"It is deeply unfortunate that there has been this incident, it was deeply unfortunate that there was the incident against Kevin Rudd's godson who was a supporter of same-sex marriage," he said.
"We had wanted the parliament to do its job and to vote through marriage equality so we wouldn't have this postal survey but we have it now and so that means our job is to make sure that everybody who is engaged in this debate does so with dignity and does so with respect directed at those who may have different views to theirs."
Opposition Leader Bill Shorten said he had phoned Mr Abbott to tell him that he was glad he wasn't hurt in the incident.
This is terrible - violence like this is never acceptable. I'm glad Mr Abbott isn't seriously injured and I've rung him to say so. https://t.co/FkSOUhObgZ??? Bill Shorten (@billshortenmp) September 21, 2017
"Ours is a campaign of hope, respect and unity. Our actions should reflect that. Violence is never acceptable," said Labor Senator Penny Wong.