Hendrix Hauwai, 17, pleaded guilty last year to the attack outside a North Shore, Auckland, supermarket, which left Ms Knight fighting for her life in hospital.
He was today sentenced to four years and nine months in prison when he appeared at North Shore District Court for aggravated wounding and assault with intent to rob.
Ms Knight and her husband Peter Thomas were in court to watch Judge Philippa Sinclair deliver her sentence, in which she described the punch as "deliberate, powerful and gratuitous".
Details of the attack can also be revealed for the first time. It emerged that Hauwai punched mother-of-six Ms Knight in the back of the head as she tried to stop him stealing a handbag from a Chinese woman. The blow sent her to the ground, fracturing her skull.
Hauwai was on bail at the time of the incident for another handbag snatch carried out five days previously.
He was bailed following an attack in Manurewa in which he kicked and punched a woman in the head as she lay on the street, Crown counsel Brian Dickey said.
The next day, September 18, he snatched a Louis Vuitton handbag from a woman in East Tamaki's 'Chinatown' area.
He was today sentenced for all three incidents together.
He was given a sentence of four years and nine months for the attack on Ms Knight, and 12 months for the other charges, to be served concurrently.
That the three violent acts occurred so closely together, and within days of being bailed, should "be of concern to the community and to the court", Mr Dickey said.
Ms Knight, 43, underwent surgery to relieve bleeding on her brain after she tried to stop Hauwai stealing a handbag from a woman outside Countdown in Northcote in September.
The incident happened in front of her young children.
Mr Dickey described her as a "brave woman" who showed "courage and selflessness" in going to the aid of another.
Both Ms Knight and her family had suffered in the aftermath of the attack, he said, particularly her two youngest children - aged 2 and 5 - who were with her at the time.
She felt she had been "taken away" from her children during her long stint in hospital.
"It has been very stressful to know that my two boys witnessed me getting punched and injured," Mr Dickey quoted from Ms Knight's victim impact statement, adding that she had felt powerless to prevent it from happening.
The two boys were also left alone while she was rushed to hospital. "Two kind people" looked after them until her mother arrived.
Hauwai's defence lawyer Kelly-Aan Stoikott said the teen did not have the "cognitive maturity" to understand the consequences of his actions at the time he committed them, but had since suffered "flashbacks of seeing one of his victims falling".
"[This is] a real and physical manifestation of the guilt this young man now carries with him," she said.
A Givealittle page set up by friends raised nearly $270,000 for Ms Knight's family.
By Patrice Dougan of NZME. News Service
