Tylann James Airey, 26, pleaded guilty to assaulting Bradley Thomas Walters on October 25 last year.

Police prosecutor Beri Kurdistan said Airey approached a man at about 12.20 pm.

"The discussion became heated, and the defendant punched the complainant in the right side of the face and then the left ear with a closed fist," Ms Kurdistan said.

After the complainant pushed Airey, he swung again but missed.

She said Woolworths staff intervened to break up the incident.

"The complainant suffered soreness to both sides of the face," Ms Kurdistan said.

The court heard that Airey attended the Launceston Police Station a fortnight later and told police that he believed the complainant had assaulted an 18-year-old associate earlier that day.

He said he had punched Walters more than once, and it was not a fight but more of a physical disagreement.

He said he used force equivalent to 5/6 out of 10.

Magistrate Ken Stanton asked whether he had taken the law into his own hands.

"Stupidly, yes," Airey replied.

"I regret it a lot, but yeh..."

In sentencing, Mr Stanton said that an assault with multiple punches to the head could lead to serious injury.

"You took the law into your own hands and decided to commit an assault because you understood something had happened earlier in the morning," he said.

"This is not acceptable.

"This is a vigilante act albeit spontaneous."

He said Airey had a conviction for four assaults as a youth but had nothing since 2016.

"This is not isolated but is out of character as an adult," Mr Stanton said.

He ordered Airey to do 36 hours of community service and comply with a community correction order for twelve months.