Promising NRL player Jamil Hopoate has been sentenced to at least 12 months jail for assaulting a man outside a northern beaches hotel.

But lawyers for Hopoate almost immediately indicated they would appeal the sentence and have launched an 11th-hour bid for bail, but this application was rejected by the magistrate.

In February this year, in an attack described by Downing Centre Local Court Magistrate Jane Mottley as "savage and unprovoked", the 20-year-old Manly Sea Eagles player and a group of friends punched and kicked Alexander Christie outside the Ivanhoe Hotel.

When another man, Timothy Blackett, tried to intervene he was "tossed aside like an unwanted plaything".

Hopoate later pleaded guilty to two counts of assault occasioning actual bodily harm in company over the attack.

In an earlier hearing watched closely by Hopoate's famous father John, the 20-year-old's lawyers argued that he should be spared a full time custodial sentence because of his age and the likely effect on his mental health.

But Magistrate Mottley disagreed, finding that "the only appropriate sentence is one of full-time imprisonment".

"Mr Hopoate and his co-offenders set out to exact revenge on a person or persons," Magistrate Mottley said in a scathing set of remarks on sentence.

"If ever there was a case of someone being in the wrong place at the wrong time it was Mr Christie.

"As someone from the northern beaches area he may well have cheered Mr Hopoate's team from the sidelines.

"But he was punched, kicked and rendered unconscious. There needs to be accountability for this kind of behaviour and recognition for the harm done to the community."

Hopoate was sentenced to a maximum 18 months jail with a minimum 12-month non-parole period.

He was also placed on a two-year good behaviour bond for the second assault on Mr Blackett.

Hopoate was hugged and kissed by his father John before removing his jewellery and tie in preparation to be taken into custody by corrections officers.

Hopoate returned to court less than an hour later with his lawyers indicating they would appeal the decision and asking for his immediate release on bail pending that appeal.

But Magistrate Mottley gave the bail application short shrift, declaring that the appeal had "no reasonable prospects of success".

She also said that there was an unacceptable risk that Hopoate would fail to appear at court if released as well as an unacceptable risk that he would commit a further offence.

The application was refused and Hopoate was taken back into custody.