A teenager who punched a policeman in a drunken brawl had his penalty almost trebled to send a "strong message" that youths faced detention for serious assaults on officers at out-of-control parties.
A magistrate gave the 17-year-old three months detention for the assault but the youth applied for a review in a bid to have the sentence replaced with a non-custodial option so he could keep working.
Instead, Children's Court President Denis Reynolds increased the term to eight months.
In a decision handed down on Friday, Judge Reynolds said police should get the full protection of the law when asked to try to restore peace and good order.
"Parties at night which deteriorate to young adults and/or children engaging in violent and other antisocial behaviour in and about houses, community facilities and public streets, and then defying police and being aggressive towards police . . . have become a serious problem in Perth," Judge Reynolds said. "Usually those involved have consumed too much alcohol."
The youth, who has previous offences, had up to 10 cans of mixed spirits before police tried to break up spot fights among up to 100 youths at a park in Spearwood on April 22.
The teenager punched the officer in the face after the policeman fell to his knees during a scuffle.
The officer lost consciousness, had mild concussion, extreme discomfort and soreness, serious dental injuries and had to wear a mould to realign his jaw.
Judge Reynolds said the assault was serious gratuitous violence against a police officer carrying out his duty to restore peace and good order and when he was vulnerable on the ground.
He said rehabilitation was always a significant consideration but in cases this serious there needed to be a strong message to young people that such behaviour was totally unacceptable and could result in immediate detention and a lengthy term.
"That message needs to reverberate through the cohort of young people who choose to drink to excess and create serious public disturbances," Judge Reynolds said.
WA Police Union president George Tilbury commended Judge Reynolds' "tough stance" and hoped it would lead to courts cracking down on assaults on police.
"This is yet another example of the lack of respect shown by juveniles towards police," he said.