This showdown is personal.

Like most sporting grudges, the dislike between the Crusaders and Chiefs, which has become perhaps the pre-eminent rivalry in New Zealand rugby, has its roots in the success of the two franchises, plus a little bit more besides.

Crusaders coach Scott Robertson, in his first year at this level, struck a conciliatory note this week ahead of tonight's semifinal in Christchurch when he paid credit to the Chiefs' achievements under Dave Rennie, who will leave to coach Glasgow once this season is over.

But for Rennie, there was no such hesitation in telling it like it is. Asked by Radio Sport whether there was "hate" between the teams, Rennie responded with utter honesty.

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"That's pretty accurate, I'd say. In the end, they've won so many titles and I guess we wanted to really stand up to them six years ago," he said.

"There have been some titanic clashes - they're always physical, all the Kiwi games are. This will be no different and there's more on the line. It should be a pretty brutal affair ... "

Rennie has done an extraordinary job in turning around the Chiefs' on-field performances since taking over in 2012. They won their first title that year, and another the year after, and under him, they have been a stubborn and difficult side to break down; a bit like their coach.

Since 2012, the Chiefs have viewed the Crusaders as a talented team but one that possesses a soft centre. Stand up to the playground bully, the theory has gone, and the bully will back down, and really, that is probably the best way to approach an All Black-stacked franchise which has won seven titles.

The Chiefs' success against the Crusaders over the years - they beat the red and blacks in two semifinals in Hamilton in 2012 and 2013 and have enjoyed a good run since until their loss to their rivals in Suva this season - has been built on a relentlessly physical approach, one that often stretches the laws of the game.

Rennie's team is often on the wrong side of the penalty count and in those early years were often criticised for their tactics of holding and tackling opposition players beyond the breakdown.

As for the Crusaders, under previous coach Todd Blackadder they became annoyed at what they perceived to be niggly, cynical tactics from the Chiefs, and in Crusaders headquarters there was disquiet at Rennie's recruitment practices.

The theory was that the Chiefs took a scattergun approach to signing young players from the Crusaders catchment area.

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The Crusaders built their success in their early years around taking unwanted players from other franchises and turning them into world class players - think Norm Berryman, Norm Maxwell, Ron Cribb, the list goes on, but the luring of promising players either from the Crusaders academy or straight out of school has occasionally angered the southerners.

With so many All Blacks clashing in the sudden death semifinal match at AMI Stadium from 7.35 tonight, including test locking partners Sam Whitelock and Brodie Retallick, a new chapter in this rivalry is about to be written.

There will be anger and there might even be hatred; required viewing, in other words, for those who like their rugby to be relentless, skilful and, above all, intense.