"We've worked pretty hard on the defensive aspect of our game," Hammett said. "Pretty clearly we had some issues from set-piece. Some of it is system-orientated and some of it individual. So we've worked hard at that during the week."
Hammett has named an unchanged starting XV to the one which lost to the Chiefs in Hamilton.
Of interest will be the match-ups between halfbacks Perenara and Piri Weepu, and first-fives Barrett and Michael Hobbs. The latter gets the nod ahead of Gareth Anscombe, who has been dropped from the match-day squad.
The Chiefs are resting Taumalolo in favour of Toby Smith for their match against the Lions in Pukekohe on Saturday. Michael Fitzgerald replaces Brodie Retallick at lock, Asaeli Tikoirotuma replaces Tim Nanai Williams on the left wing and Kane Thompson is back at No8.
Blindside flanker Liam Messam is unavailable due to a rib injury. Sam Cane will wear the openside flanker's jersey, with Tanerau Latimer moving to the blindside.
The unforced changes were predictable given the poor recent form of John Mitchell's Lions. "As we are only half way into the competition we are using this game to give some players who have not had much game time an opportunity they deserve," coach Dave Rennie said.
Sharks' coach John Plumtree has put the focus on the Highlanders' breakdown tactics ahead of the match in Durban on Sunday morning (NZT).
The Highlanders were penalised heavily in their last match, a narrow win over the Cheetahs in Bloemfontein, with Andrew Hore sinbinned for a ruck infringement.
Plumtree has called on referee Steve Walsh to follow Marius Jonker's lead in the Cheetahs match and keep a sharp eye out on any negative play at the breakdown.
"The Highlanders were pretty impressive against the Cheetahs last weekend," Plumtree told the Sharks' website.
"They are very aggressive at the breakdown and I thought Marius Jonker penalised them pretty hard for going off their feet which was pleasing to see, and hopefully we'll see that again this weekend - that if they counter-ruck, they have to stay on their feet. The referee was also hard on them for slowing possession down and once that area of the game was sorted out we saw an open game of rugby with a lot of points scored," he said.
"So we're hoping Steve Walsh will also be tough on that area on the weekend."
The Highlanders will be missing openside flanker James Haskell, who has been banned for three weeks for throwing punches in the Cheetahs match.
The Crusaders will hope to continue their resurgence with a victory over the Reds in Christchurch on Sunday. The grand final rematch even has the same referee - Bryce Lawrence - which proves someone at Sanzar has a sense of occasion, if not humour.
The Crusaders privately felt Lawrence was a little easy on the Reds at the Suncorp Stadium cauldron last year; the Queensland team winning a tight final 18-13. Sunday's match at the Crusaders' new 17,500-seat stadium kicks off at 4pm and is already a sellout.
The Bulls, fourth overall, begin their tough southern tour with a relatively easy match against the Rebels in Melbourne on Friday but will face stiffer challenges against the Waratahs, Crusaders, Highlanders and Chiefs.
In Canberra on Saturday night the two top teams in the Australian conference, the Brumbies and Waratahs, play off.
