A judge has admonished the state's department of corrections for what she said was a case of preemptively doling out punishment for a crime which was before the courts.
Wade Basanovic was on Friday sentenced to a 19-month jail term in Newcastle District Court for his role in a jailhouse bashing at Cessnock last year, while he was serving a prison sentence for fatally shooting a senior bikie several years ago.
With a non-parole period ending next June, it means the 32-year-old will spend only one extra month in jail after his non-parole period ends for the manslaughter sentence he has been serving for a decade.
Judge Penelope Wass said Corrective Services NSW officers had "taken it upon themselves to punish the offender" since the bashing - allegedly segregating him and moving him several times as well as serving him frozen meals he believed contained uncooked meat.
"It is not the responsibility of correctional facilities to impose a punishment for an offence that is before the court," she said.
"That conduct on behalf of the state is entirely unacceptable."
Basanovic was in his own cell when he punched an inmate more than 20 times, leaving him bleeding from the face but causing no lasting damage.
Judge Wass said Basanovic's attack was not planned and he had been provoked by the man in his cell, but his response was disproportionate and he "stepped over the line".
The affray that immediately followed in Shortland Correctional Centre's G-block was "excessive", Judge Wass said, and "appears to have little excuse".
During that second part of the incident, with the help of three other inmates, Basanovic punched the victim again, kicked him, and struck him with his elbow while holding him by his hair.
At the time of the bashing, Basanovic was most of the way through a maximum 14-year jail term for killing senior member of the Hell's Angels outlaw motorcycle gang, Zeljko "Steve" Mitrovic.
He was initially charged with murder but a jury found he acted in self-defence. Basanovic's father, who the court heard on Friday joined an outlaw motorcycle gang in the early 1990s, was convicted of murder over the shooting.
