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Curry had never played as a first-team number eight for his club Sale before switching to the position for England

Guinness Six Nations: England v Ireland Venue: Twickenham Date: Sunday 23 February Kick-off: 15:00 GMT Coverage: Live radio commentary on BBC Radio 5 Live Sports Extra and online; text commentary on the BBC Sport website and app. Live on ITV.

The spotlight would perhaps be less stark on Tom Curry in another year. Or another team.

But the 21-year-old is taking his first steps as a number eight on the international stage having played a starring role at flanker in England's run to the World Cup final.

England head coach Eddie Jones decided against bringing in a specialist number eight to replace injured talisman Billy Vunipola, putting his faith instead in Curry making a rapid transition.

"I don't think it is a big change," Curry told BBC Radio 5 Live.

"I like to stay true to myself. Eddie's been good, the coaches have been good, the players have been good, so I'm excited to learn."

On Sunday, Curry faces arguably his biggest test yet when he comes up against an in-form Ireland side with CJ Stander, a British and Irish Lion in 2017, at the base of their scrum.

So what is Curry getting right and wrong in his new role?

Ball-carrying ballast

Curry, left, has stepped in after Vunipola (right) was ruled out for the duration of the tournament with a broken arm

The biggest difference between Curry and the man he is replacing - Vunipola - is the most obvious one.

Curry weighs in at 15 stone eight pounds according to England's own stats. external-link

Vunipola, just three centimetres taller, packs 19 stone 12 pounds onto his frame.

"Unless I'm putting on an extra 30kg I'll struggle to be Billy," Curry admitted. "There are going to be slight differences between how we play defensively and attacking-wise at the breakdown."

So how much do England miss that heft? The signs were not good early in England's opening match against France.

With fewer than four minutes on the clock and the scoreline blank, England had forced France to retreat to their own five-metre line following a succession of big carries from Sam Underhill and Courtney Lawes.

But just when a charging Vunipola might have punctured the remaining French defence, Curry came up short.

Curry, rather than the stationary Marler or wider Tuilagi, is George Ford's obvious power-carrying option

Curry comes onto the ball at pace...

...but France centre Gael Fickou, fast up in defence alongside Antoine Dupont, is confident enough to go high on Curry, succeeding in dislodging the ball. France duly clear though a Romain Ntamack kick

Admittedly from a small sample of two rounds of the Six Nations, Curry is the least effective ball-carrier when compared with fellow number eights Gregory Alldritt, Stander and Taulupe Faletau, according to Opta's stats.

Curry Stander Alldritt Faletau Mins played 160 158 160 132 Carries 24 23 33 13 Metres made 34 36 101 31 Average gain 1.4m 1.6m 3.1m 2.4m Clean breaks 0 1 2 0 Defenders beaten 1 4 5 5

But Curry says in the absence of Vunipola, other back rows may share the ball-carrying load: "It's a unit and we work as a team to fulfil what the back row does as a whole.

"It might not be that the eight does all the ball-carrying now, maybe the six has to do a bit more. We speak about it as a back row, we're very fluid about it. We all want to play to our strengths."

And the signs are that Curry is eating up more ground as the competition goes on.

After making just 10m from 14 carries against France, he managed 24m from 10 against Scotland.

Control at the back of the scrum

"What really changes is at the base of the scrum," adds Curry.

"We're doing a lot of drilling during the week and contested scrums but it changes during the game. As a back row, it's all about working as a unit.

"Part of that is my ability I've had as a flanker, you're not going to take away from that. You've got to make sure I adapt in certain bits and add to that balance in the back row."

Curry's naivety at the back of the scrum was exposed in the 11th minute of England's Six Nations opener in Paris.

In his usual position at flanker, Curry would have only a passing interest in the route the ball takes to the back of the scrum.

However, at number eight, he was caught out as Jamie George hooked the ball through a channel between Charlie Ewels and Sam Underhill and England's forward-moving front row meant he had to react quickly.

He switched his position to the other side of Ewels, but it was too late...

... the ball broke loose, Dupont pounced and a promising platform was lost.

However, that part of his game was improved in tricky conditions in Scotland.

After scrum-half Willi Heinz put the ball into a scrum in midfield in the first half, Curry was alive to the danger of the ball shooting out the back, adjusting his bind to get a better view of the situation.

He kept control as Scotland got a counter shove on....

...and Heinz, in contrast to Youngs in Paris, had plenty of time to pick his option.

Harlequins and England scrum-half Danny Care says Curry could be targeted by Ireland's number nine Conor Murray, another to have worn the British and Irish Lions shirt.

"As a scrum-half, you want to go up against an inexperienced number eight," said Care on the Rugby Union Weekly podcast.

"If your scrum gets parity, that's where the nuances of being a number eight might come unstuck against an experienced scrum-half like Murray.

"Positioning in the scrum, the way they keep the ball away from the scrum-half - if he gets that wrong, Murray is very experienced to be able to have a go.

"But Tom Curry is a wonderful rugby player, you could play him anywhere on the park and he would play well. He is doing an absolute job for England at the moment."

Breakdown expertise

Curry specialises in getting to the breakdown first to slow down opposition ball or, preferably, steal possession for England

In last year's Six Nations, Curry led England's turnover tally, nabbing possession five times across the campaign.

Alongside heavy-duty runners Vunipola and Mark Wilson in the back row, he was freed up to play the 'fetcher' role, sniffing out isolated opposition ball-carriers.

Has that part of his game been restricted by his new number eight responsibilities? He says not.

"At eight you might find yourself in different positions but your ability to affect the breakdown, if it's there you're still going to do it," Curry explained.

Certainly he has not matched the levels of Sunday's opposite number Stander.

Stander was shifted in the opposite direction to Curry, moving from eight to the flank, before an injury to Caelan Doris in the fourth minute of their win over Scotland on the opening weekend brought him back to the base of the scrum.

He has been as stubborn as a limpet at the breakdown since.

In the 66th minute of the win over Scotland, he clocked that Jonny Gray was taking the ball into contact without any substantial support.

He was over the top in an instant...

...and would likely have had the turnover had referee Mathieu Raynal, spotting Iain Henderson failing to roll away, not awarded the penalty the other way instead.

Stander got his moment soon enough though.

With just two minutes left and Scotland hammering away metres from the Ireland line in search of a game-tying converted try, Stander first formed part of a three man gang-tackle to stop Jamie Ritchie and WP Nel's combined charge.

He then realised Scotland had shifted the point of attack with an offload to Hamish Watson and quickly moved on to the next task.

Having beaten team-mate Robbie Henshaw and Scotland replacement Ben Toolis to the ball, Stander's rock-solid, limbo-low body position survived a couple of clear-out attempts to secure a vital turnover.

Stander has a tournament-leading five turnovers, all from 'jackalling' over the top of the breakdown.

Curry Stander Alldritt Faletau Turnovers won 2 5 2 1 Turnover conceded 1 0 2 0 Penalties conceded 1 3 1 1 Statistics courtesy of Opta

While Curry's clever coverage of the backfield has helped him get closer to some isolated runners in the wide channels, he will probably have to go toe-to-toe in close quarters with Stander on Sunday.

England's alternatives

Alex Dombrandt, Sam Simmonds, Nathan Hughes and Ben Earl have all been mentioned as contenders for England's number eight position

If Jones had wanted something closer to a like-for-like replacement for Vunipola, he did have options.

Nathan Hughes was the back-up in the 2019 Six Nations but has since fallen out of favour while the hard-running dynamism of Saracens' Ben Earl has been used sparingly from the bench in this season's tournament.

Meanwhile, Exeter's fleet-footed Sam Simmonds has been overlooked and Alex Dombrandt - the Premiership's player of the month for January after improving his output to eight tries from 16 matches this season - remains uncapped.

Curry himself admitted he has needed Vunipola's help learning "the nuances" of the position, with the player he is filling in for "picking up on things you don't get taught as a kid".

But Jones seems to be taking Vunipola's absence as a chance to rebalance his back row, prioritising mobility and breakdown smarts over the ability to bust tackles and make clean breaks.

His metrics for measuring Curry's success as a number eight may be very different from those above.