A MAN has been injured after fights broke out in the grandstands during Collingwood's 19-point win over Carlton at the Melbourne Cricket Ground on Saturday.

Separate fights broke out at the end of the game, with one spectator describing it as "Collingwood (and) Carlton supporters just full-on punching each other".

One man was treated for minor injuries, and police and security stepped in to prevent further fights, Victoria Police said in a statement.

The injured man did not want to make a report to police, but officers spoke to the alleged offender and released him pending further inquiries.

A woman at the game named Robin told radio station 3AW the fights broke out in an area full of Carlton supporters.

"There were four fights, four full-on punch-on fights where people were knocked out," she said.

"And security just didn't react quick enough, so the members of the public had to get in, including me, to stop these fights.

"I missed the last five minutes of the game because I was breaking up fights."

However, a spokesman for the MCG said: "We are comfortable with our security's response along with that of police.

"Our security and police deal with these incidents as they occurred," he said.

"If police charge someone, we will fully cooperate."

The AFL has been contacted for comment on the incidents.

Crowd disturbances also made news after the final siren of the season-opener between Carlton and Richmond, which AFL CEO Gillon McLachlan described as 'unacceptable'.