Dunedin - Scrumhalf Aaron Smith, hailed as the standout find for the All Blacks this year, has been benched for disciplinary reasons for Saturday's Test against the Springboks in Dunedin.

The dropping of Smith, the first choice scrumhalf in all six Tests the All Blacks have played in 2012, was the biggest surprise among the four changes for the fourth-round Rugby Championship game.

Hansen said Smith needed to be disciplined but would not reveal what he had done.

"Unfortunately for Aaron Smith we've got a strong focus on recovery and he broke a protocol in that area last week, so that made him ineligible for selection for the first XV," Hansen said.

"There's nothing to elaborate on. He just broke a protocol that's non-negotiable and the consequence is you don't start in the XV if you break it."

Smith's demotion earns a recall for 62-Test veteran Piri Weepu, who produced a stirring performance when he came on for the last quarter of last week's Test against Argentina.

The other changes to the All Blacks side which beat the South Americans 21-5 see lock Sam Whitelock, flank Liam Messam and hooker Andrew Hore promoted to the starting line-up.

Smith, who possesses the swiftest pass in New Zealand, which has been credited with giving his backs an extra edge, has started in all six previous Tests the All Blacks have played this year.

But coach Steve Hansen indicated no one in the side could rest on their laurels despite the All Blacks being unbeaten after three matches of the Rugby Championship.

"At the halfway stage of the new Rugby Championship we are very happy, from a results point of view," he said.

"There is a second challenge we have set ourselves - to constantly improve our game - and in that regard we are not the finished product."

The return of Messam is not a surprise after Hansen rated him the leading blindside flank. He gave Victor Vito a start last week while Brodie Retallick did not make the most of his start against Argentina and slips behind Whitelock.

Among the replacements, Charlie Faumuina keeps out Ben Franks as the back up prop and Tamati Ellison takes over from Ben Smith in the back utility role.

Teams:

New Zealand:

15 Israel Dagg, 14 Cory Jane, 13 Conrad Smith, 12 Ma'a Nonu, 11 Julian Savea, 10 Aaron Cruden, 9 Piri Weepu, 8 Kieran Read, 7 Richie McCaw (captain), 6 Liam Messam, 5 Sam Whitelock, 4 Luke Romano, 3 Owen Franks, 2 Andrew Hore, 1 Tony Woodcock

Substitutes: 16 Keven Mealamu, 17 Charlie Faumuina, 18 Brodie Retallick, 19 Victor Vito, 20 Aaron Smith, 21 Beauden Barrett, 22 Tamati Ellison

South Africa:

15 Zane Kirchner, 14 Bryan Habana, 13 Jean de Villiers (captain), 12 Frans Steyn, 11 Francois Hougaard, 10 Morne Steyn, 9 Ruan Pienaar, 8 Duane Vermeulen, 7 Willem Alberts, 6 Francois Louw, 5 Juandre Kruger, 4 Flip van der Merwe, 3 Jannie du Plessis, 2 Andries Strauss, 1 Tendai Mtwarira

Substitutes: 16 Tiaan Liebenberg, 17 Dean Greyling, 18-Andries Bekker, 19 Marcell Coetzee, 20 Johan Goosen, 21 Juan de Jongh, 22 Pat Lambie