A teenager has pleaded guilty to attacking Lucy Knight as she intervened during a bag snatch outside an Auckland supermarket.

Hendrix Hauwai pleaded guilty to aggravated wounding and assault with intent to rob after the incident on September 23.

This morning at North Shore District Court his lawyer spoke about the 17-year-old's intention to make amends but details were suppressed by Judge Lawrence Hinton.

Ms Knight underwent surgery to relieve bleeding on her brain after she tried to stop Hauwai stealing a handbag from a woman outside Countdown in Northcote.

The mother of six fell and fractured her skull in the incident.