Analysis: Wayne Barnes will need to watch Welsh scrum weak link Gethin Jenkins
Samson Lee may still be a bit raw at test level, but Gethin Jenkins is the man for Ireland to target in Cardiff this weekend.
At his prime, Jenkins was as good as any loose head in the world. He could carry, tackle, clear out, and, most importantly, scrum.
It was the set-piece where he was most destructive, but over the last few years he has lost his power, and he looks to be living on borrowed time.
He's likely to face off against another man fighting time this Saturday, in Mike Ross, but the Irish tight-head has shown during these championships that he's not ready to give up his jersey just yet.
Jenkins struggled against Dan Cole's technique and power on the opening weekend against England, and his side of the scrum has continuously been messy over the three games Wales have played.
On paper, the Welsh scrum did well against France. They won 10 of the 11 scrums on their own feed, conceding just one penalty at the set-piece in the whole game.
However, much of that was down to referee Jaco Peypar, who was far too lenient, blowing for just two late penalties and one free kick in the game's 14 scrums.
On the opening scrum of the day, Peypar had a chance to stamp his authority, but chose to reset rather than penalise after Jenkins' crooked driving had caused the scrum to collapse.
On the re-set, Jenkins' angle of driving was arguably even more pronounced, as you can see below. His side eventually collapses, but with the ball making its way out the back of the scrum, Peypar chooses to turn a blind eye, one of many he would turn that day.
However, he made a real mistake on the third scrum which could have resulted in an injury to himself.
As the packs crouched, Lee's body was too high, as he rested his head against the gap between Ben Arous and Guirado. His head was above his waist, compared to Ben Arous' body, which was parallel to the ground.
It meant that when the packs engaged, Lee's head remained outside the scrum. The result was that he was driven backwards instantly, but, spotting that Lee's head was essentially trapped, the referee blew to re-set the scrum.
As you can see below, Ben Arous' momentum drives him through Lee, who was lucky to escape uninjured. One more reason for props to keep their bodies square and straight.
On the reset, the Welsh come under a lot of pressure before eventually getting the ball out of the scrum, but they were extremely lucky to avoid conceding a penalty with Jenkins again bending the rules, while Lee could also have been punished.
The successful French drive came largely down to the excellent body position of Ben Arous. His angles were perfect; 90 degrees between body and legs, and around a 120 degree bend at the knees.
However, Jenkins also has a lot to answer for here, as he drops his bind completely. You can see the bandaged left arm of the prop on the right side of the picture below. He is struggling with the power of Rabah Slimani and turning inwards, eventually removing his bind completely. However, again, Peypar keeps his whistle in his hand.
The tight-head lost his footing and scrummaged on his knees for a few seconds, right in front of the eyes of the referee, who had clearly decided to let the front rows police themselves.
However, the same couldn't be said for Jenkins though, who continued to have great difficulty up against Slimani.
In this scrum, we can see how Jenkins angles in dramatically on Slimani, which results in the scrum arcing down the blindside of the pitch, and the Welsh almost score a try from it.
Here's how the packs lined up as they engaged. There is a slight angle, but Jenkins is relatively straight on his opponent.
Note how the line he's taking is almost perpendicular to that of his teammates, and also keep an eye on his bind. He's actually turned so far against the grain of the scrum, that he's no longer binding on Slimani, instead holding onto the arm of flanker Bernard Le Roux.
In his final scrum before being replaced by Paul James (who isn't on the bench for the Ireland game, Rob Evans steps in), Jenkins does just that, taking advantage of the size and immobility of the behemoth Uini Atonio.
By scrummaging low to the ground, and keeping his body straight and his angles in check, Jenkins forces Atonio to drop to the ground, and scrum on his knees. In keeping with the game, Peypar did not reward him with the penalty he deserved, but Wales did secure possession comfortably.
Similar to Jenkins last time around, James executed his fundamentals perfectly, and playing to his opponent's weaknesses. Atonio's monstrous size means that by scrummaging low and straight, the Frenchman loses most of his power.
It's a difficult one to call. James does well, and gets a good drive on Atonio, but the scrum pops up on the referee's side, and it looks like Lee is holding the arm of Debaty. A hard one to call, so we'll give the referee the benefit of the doubt.
In the photo below, we can see how hooker Kayser loses his bind from Debaty, who has driven in at an angle on Jarvis, whose head is sticking out of the scrum.
And with Wayne Barnes due to take the whistle this Saturday, you can be guarantee we'll be seeing more penalties, against both sides, whether correctly or incorrectly.
Targeting Gethin Jenkins is vital. Barnes tends to make up his mind early on in games, and should Mike Ross stamp his authority on his opposite man in the opening few scrums, it could be a fruitful afternoon afternoon for the Irish scrum.