Speaking after the match, Bath head coach Mike Ford couldn’t put his finger on why Bath lost on Saturday.
But with half of Leinster’s 18 point total coming as a direct result of penalties conceded at the scrum, the answer is pretty obvious.
With third-choice tight-head Kane Palma Newport up against the best loose-head in the world in Cian Healy, and Paul James thrown in to start after four weeks out with a fractured thumb, Bath were always going to be up against it. Still, few could have imagined just how much of a hammering they would take.
Strangely though, Bath looked dominant on the opening two scrums, with Palma Newport taking advantage of some sloppy positioning from Healy to drive him back.
On the opening scrum, he times his drive perfectly, and puts Healy under a lot of pressure, but it all stems from his excellent body position, as you can see below.
With Leinster feeding the scrum, Palma Newport waits until the exact moment that Cronin attempts to hook the ball, and begins pumping his legs furiously, catching Healy out and sending the scrum back on his side.
Watch how, despite continuously pumping his legs, Palma Newport maintains a straight back, parallel to the ground. One without the other would not have sent Healy backwards.
Two minutes later, he did even better, forcing Healy to collapse and give away a penalty.
Healy’s body position is poor compared to his opponent. While Palma Newport’s back is straight, Healy has far too big a curve in his, which takes away so much of his power.
It’s vital that a prop gets a good pelvic tilt to keep his back parallel to the ground, and in the end, Healy collapses the scrum, with Jerome Garces rightfully awarding Bath a penalty.
At this stage, it looked like Leinster were in for a dogfight at the set-piece, but from here it was as if they flicked a switch, dominating the scrum for the next 70 odd minutes.
They blew through Bath at the next scrum, as James conceded the first of several penalties he’d give away for driving crooked, but while we were not given a replay of that side of the scrum, Bath could just have easily been penalised on the tight-head side.
As we can see below, Palma Newport and Healy are both lined up straight and square to one another as Isaac Boss gets ready to feed.
But as soon as the  ball comes in, Palma Newport begins to drive up into the air, with his head considerably higher than his hips, and his legs locked out.
The penalty was ultimately given against James on the far side of the scrum, and while we can’t see any of the action, Sean O’Brien’s running commentary alerts us, and Garces, to some illegal activity from the Bath loose-head.
“Look at his elbow, look at the angle! Angle, sir! Angle, Angle!”
They landed another penalty soon after, and this time it was worth three points.
Again we’ll look at the scrum’s initial position as a reference point. Watch how all the bodies are square to one another, especially the almost symmetrical positions of Healy and Palma Newport.
After getting the ball back to the feet of Jamie Heaslip at the base of the scrum, Leinster go on the attack, with Healy widening his stance, before driving straight through Palma Newport, who tries to lock out his legs and stand up, rather than go backwards.
As a reference point, compare the dead straight back Healy has here with the arched back he had when conceded the early penalty. Popping out the pelvis makes a world of difference.
However, Healy continues to power through him, and ultimately the tight-head drops the scrum by collapsing to his knees.
Leinster are in total control at this stage, and Palma Newport tries to get back on his feet before Bath are marched back again. In the end, James is pinged for driving in at an angle, and Ian Madigan slots the three points.
Leinster dominate to win another penalty before half-time, which Madigan kicks to make the score 12-6, and again it is James who’s penalised for driving in at the angle.
But, just like the previous scrums, Garces had the pick of infringements to penalise, with Palma Newport also dropping to his knees.
Here we have the initial set-up of the scrum, with both players lining up in ideal body positions.
However, Healy’s power is too much for Palma Newport, as he eventually drops his knee to the ground, before the penalty arrives.
It was the third penalty Mike Ross would win from James in the space of six first half scrums, and his scrummaging was the direct reason for six of Leinster’s eventual 18 point total.
It’s a remarkable turnaround for Ross – how many other 35-year-olds have played their way back into a starting position after being dropped from the squad altogether, before putting in such an influential performance on their return?
He was even unlucky not to win a fourth penalty from James just after half time, as the Bath loose-head was guilty of driving early and angling in.
Here’s a view of the scrums as they bind on one another. Watch the yellow line running through the centre of the scrum. This will be a reference point for how far it moves forward.
However, we can see from the photo below just how much ground James steals on the engagement, a nod to the old days of hit and chase in the front row.
In the gif below, we can see just how much room James steals on the hit.
The extra couple of yards does little to help James though, who should arguably have been taken off at half time, such was the hammering he was taking.
When Ross begins to get on top, James begins to drive inwards yet again, to the extent where he is driving almost perpendicular to the Leinster scrum. Bath recover possession, lucky not to conceded another penalty in a kickable position.
Ross departed for a fresh Marty Moore, whose first action was to win a final penalty from the floundering Paul James, which was again kicked between the sticks by Madigan.
Once more, we can clearly see the difference in directions. Moore is square and straight, while James has popped his hips out and is driving inwards.
As Leinster move forward at will on Healy’s side, Moore acts as an anchor, holding his position while James tries to turn him inside. It’s a very clever piece of scrummaging, when the natural inclination for him is to try go forward.
Instead, he holds his spot, and Leinster are better off for it.
James was replaced soon after, but his replacement Nick Auterac also got punished by Moore at the scrum.
The difference in body positions is clear. Moore is perfect, 90 degrees at the hips, and around 120 degrees at the knees, while Auterac’s legs are locked out, meaning he can’t get any power into his drive.
Again, Leinster win a penalty, making it the five penalties in just 10 scrums.
It seems to be given by Garces side of the scrum, and I suspect it is for Dave Attwood driving upwards from the second row.
We can see below how Palma Newport has been lifted off his feet into the air, with Attwood standing upright beside him.
With Palma Newport being consistently driven backwards by Healy, Attwood tried to stem the flow of the scrum by driving upwards, dangerously lifting his prop into the air. While Healy could have also been driving upwards, it appears unlikely for a number of reasons.
For starters, Healy had been driving straight and square on Palma Newport for the whole game up until that point, and Garces had been consistently penalising James for his dangerous angles. With the referee positioned on that side of the scrum, it is likely he would have penalised Healy for doing similar.
The final three scrums were quick in and outs, with Bath’s replacement props Auterac and Nick Lahiff stabilising things.
However, the damage was already done. Five penalties, three of which yielded scores gave Leinster a fantastic platform to work from, and if Ross and Healy perform similarly in Marseilles, this Leinster side may well have a chance.
