Scotland v Wales: The battle at the breakdown is likely to prove decisive this afternoon, which is why both teams have spent the week doling out advice to the Irish referee, Alan Lewis.
The Wales head coach, Gareth Jenkins, has become obsessed with the way Australia and New Zealand apply pressure at the contact area by using guards to push opponents out of the way to protect their own ball and disrupt the opposition's. He calls it counter-rucking and has hired a judo expert to help his players gain a grappling technique.
Jenkins has favoured the physical presence of Alix Popham in his back row rather than the more dexterous Michael Owen because of the importance he attaches to the breakdown. Wales have pace in the back row, with Martyn Williams a specialist openside flanker, unlike Scotland's Kelly Brown.
Wales were effective in the contact area against Ireland, using Popham and number eight Ryan Jones to squeeze the scrumhalf Peter Stringer, and, with Scotland opting for a more attacking back division than the one that confronted England, both teams will be looking for quick ball at the breakdown.
Wales moaned about Ireland's spoiling tactics in the ruck, and Scotland captain Chris Paterson, said this week it was an area where Wales had become adept at cheating in the way they held players back and knocked them out of the way, but Scottish back rows have been renowned for testing the tolerance threshold of referees. Applying pressure on officials in the build-up has become a game within a game.
It also highlights the importance of a victory to both sides. It is a year since Wales, Grand Slam champions in 2005, defeated a side in the top 10 of the world rankings. On their last visit to Murrayfield, they played with such a swagger they had the match won at half-time, but Scotland were at their lowest ebb as the reign of coach Matt Williams stuttered to an end.
Whether Scotland have the means to take the game to Wales is questionable and they have reached a defining moment under Williams's successor, Frank Hadden.
Scotland got stuck in against England but were not equipped to chase the game and, even with Phil Godman replacing Dan Parks at outhalf, they need an early lead.
While France and England were predictable at Murrayfield last year, Wales pose a different attacking threat, even if their makeshift three-quarter line lacked potency against Ireland.
Wales last Sunday were undone by an inability to improvise, failing to use James Hook at first receiver in broken play. While outhalf Stephen Jones is an excellent distributor and tactician, Hook poses the greater attacking threat.
Wales have the greater potential but still bear the scars of last year's coaching kerfuffle. There is a vulnerability for Scotland to exploit.
