The victim, who was punched six times and had her head stomped on, suffered a cracked cheekbone and eye socket, a broken nose and split lip, the Dunedin District Court heard this week.
Judge Kevin Phillips acknowledged her attacker, then aged 16, was on electronically monitored bail at the time - a decision he made.
''You shouldn't have been on bail,'' the judge conceded. ''It was against my better judgement and I have to take responsibility.''
The man - now aged 18 and understood to be a member of a youth gang after spending long stretches in youth justice facilities - had his previous case transferred from the Youth Court to the District Court.
The measure was taken so he could receive the intensive counselling required.
''You rejected anything that was put in place to help you,'' Judge Phillips said.
Things went spectacularly awry on May 6 last year.
While serving the sentence, the teen was with his brother on Hillary St after they had seen a party advertised through Facebook.
On the street the pair approached a 16-year-old boy and ordered him to empty his pockets.
One of them punched the boy in the face, knocking him out.
As he lay on the ground, the brothers took his phone and wallet.
Only 10 minutes later, the defendant and friends were driving in Cumberland St and they stopped after spotting a group of five students carrying alcohol.
One of the group complied with demands to hand over a box of beer, while the defendant grabbed a box of cider from another.
They asked one of the students to give up his wallet and cellphone and when he refused, both brothers punched him in the face.
As they prepared to leave the area, the defendant noticed a woman trying to photograph the car they were in.
He tried to wrestle her phone from her before leaving the scene.
When the youth appeared in court, Judge Phillips granted him electronically monitored bail to his father's home.
On July 11, 2017, while at a South Dunedin training centre, the defendant approached a woman who ''had been saying bad things about him''.
The ''ferocious'' assault began with six punches to the face, which knocked the victim to the ground.
As she tried to protect herself, he kicked her in the head as hard as he could and followed it up with two stamps to the temple.
While the judge condemned the defendant for his crimes, he lamented his personal circumstances. The court heard the man had gone into care at the age of 2 and was moved 13 times between homes within a year.
At 13 years old he was living in a car.
Gangs, violence and drugs were the norm, Judge Phillips said.
''You're a young man who has had no chance or opportunity in life whatsoever and I feel very sad about that,'' he said.
The defendant was jailed for three years and two months.
