A large group of youths, believed to be armed with machetes, got into a fight after NRL Victoria's Harmony Cup at Broadmeadows in Melbourne's outer north on Saturday night.
A 19-year-old man was found nearby with serious stab wounds to his torso.
Detective Sergeant Matthew Feben said there were up to 1000 people dispersing from the community rugby league event when the fight broke out.
"It was quite heavily populated in the area at the time," he told reporters on Sunday morning.
"There was a large group leaving the area.
"Police are investigating the possibility they may have been in attendance at that event."
Offenders were described as being in their late teens and armed with machetes in an initial triple zero call, Det Sgt Feben said.
The 19-year-old victim from the Hume area is in a stable condition in hospital but has been uncooperative with police.
No arrests have been made with the suspects driving away before police arrived.
Detectives are investigating whether the fight was linked to another incident on Friday night when youths armed with machetes were spotted running through the three-day event.
The Harmony Cup is a nine-a-side competition that gives players and volunteers a chance to represent their country of origin or local community.
Det Sgt Matthew Feben was very concerned by the "appalling" behaviour, describing the event as otherwise peaceful.
"It's completely unacceptable in any location for youths or anyone to be armed with a machete," he said.
"Police are putting lots of time and energy to getting these weapons of the street.
"Over the past 12 months, 13,000 edged weapons have been seized, which equates to 47 per day."
Another 5200 machetes have been collected from disposal bins and roughly 3400 taken off shelves as part of a state ban on their possession and sale, Premier Jacinta Allan said.
"We are getting more of these dangerous weapons off our streets than any other state," she said
"All up more than 20,000 of these dangerous weapons."
Ms Allan acknowledged machetes were causing grief and concern in Victoria but maintained the state was safe despite crime rates hitting a 20-year high.
The premier reminded Victorians the three-month machete amnesty finishes at the end of November, with prison time and "hefty" fines to follow.
It comes as the Victorian Chamber of Commerce and Industry launched a survey to attempt to quantify the cost of criminal activity and anti-social behaviour for businesses.
The survey is the first of its kind by the peak body, responding to anecdotal reports of theft, damage and safety concerns.
It will deliver data on the scale of the issues but also focus on solutions, with chief executive Sally Curtain warning leaders not to ignore it.
"We need to turn this around," she told Melbourne radio station 3AW.
The survey will remain open to all Victorian businesses until November 11.
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