Terrifying Springboks bruisers primed to exploit Ireland's vulnerable front row at World Cup

Less a tactic than a warning to the rugby world, the introduction of seven Springbok forward replacements in one go cast an awesome shadow across the World Cup on Friday.

The darkness spread west from Twickenham to these shores but, more importantly, the risk of it casting east across France, as far as Paris on September 23, remains all too real.

It is on that Saturday night that Ireland face the game that will define not merely their pool fate, but which looks like determining their World Cup ambitions.

And after what the South Africans did to New Zealand in London, the magnitude of that challenge is now clear. Its dimensions are forbidding - and nowhere as vividly imposing as in their forward options.

Springbok teams are defined by their packs. In a rugby culture that has been adorned by some of the most skilful players in the history of the game, its essence is still best captured in steaming props, towering locks and loose forwards as quick and ruthless as dipping scythes.

That is why, despite the emphatic scoreline and the back-line dazzle that bewildered New Zealand, the game's most dramatic moment came in the 47th minute.

That was when Leinster head coach-in-waiting Jacques Nienaber introduced a new front row, a new second row, a new blindside flanker and a fresh No8.

They were leading 21-0 at the time in a contest they would go on to win 35-7, but this was an expression of dominance designed to deflate New Zealand in the short term - but which looked awfully like a statement of power intended to resonate all the way to France, too.

World-class talents like Ulsterbound Steven Kitshoff, the wonderful hooker Malcolm Marx, and the team's enforcer Eben Etzebeth, were replaced to no weakening effect by stars of the calibre of Ox Nche, Bongi Mbonambi, and RG Snyman.

Observers were left scrambling for precedents. It's become common for Test teams to replace entire front rows, and it was the 2019 World Cup-winning South African team that used their famed 'Bomb Squad' to such effect: the arrival of a new front row provided critical leverage in game after game. The effect it had on England in the final will not be easily forgotten, as a team already pummelled by the South African starters were denuded of all hope, and clemency, when the subs rolled on. But to introduce almost a new pack at one time is unheard of.

This is mainly because Test teams don't go for a seven-one split among their eight replacements.

The convention is five-three, which means five forwards and three back-line players, the latter usually comprised of a scrum-half, out-half and utility back. The five forwards must include two props and a hooker, with a second row and loose-forward option making up the set.

Some teams favour six forwards and two backs, depending on the opposition but, more importantly, the depth of their own resources.

It is invariably a heavyweight power like South Africa or France that can indulge in such a selection. But seven-one, forced on Nienaber by the late withdrawal of back-three cover Willie le Roux, now looks a viable option for the Springboks - even if it is heavily caveated. It makes enormous demands on the starting back-line players, with only one back among the replacements.

Not only must they stay fit, but as many of them as possible must be able to cover more than one position.

This was the case with the South African team that started against New Zealand, but that tactic will not always work so cleanly.

Damian Willemse had a fine game at full-back in London, for instance, but he had an awful evening in Dublin last November when he played at out-half.

The man in the No10 shirt against New Zealand, Manie Libbok, barely put a foot wrong, but on URC duty for the Stormers he has looked wildly erratic.

What the Springboks will seek to do is grind down their opponents in the tight and limit the room for variables elsewhere, look to kick their penalties and snaffle any tries that come their way.

It's not foolproof, but with their forward resources - and the lingering suspicion they will find a way to get Handre Pollard, their star No10, off the stand-by list and into their final squad - it will be a tactic difficult to face down.

First to try and do so will be the Scots on September 10, the day after Ireland's opener against Romania. The nature of that Scottish task is now clear, and few would swap places with them in Marseille.

But they will, at least, have two straightforward fixtures thereafter, playing Tonga and then Romania, before facing Ireland in the final round on October 7.

Even if they have lost to the Springboks, the Scots will have four weeks to piece themselves back together, whereas Ireland will have a fortnight after they play South Africa in round three.

Those contrasting recovery periods will matter, because whatever else South Africa will bring, bruising power is guaranteed.

It is why, for all the more subtle and well-executed elements of their All Blacks' rout, it was that power game, encapsulated in the seven-man substitution, that mattered most.

And it came the night before Cian Healy became the most luckless casualty of Ireland's tournament preparations.

Confirmation that he had suffered a serious calf injury was only delivered to the Ireland team hotel minutes before the World Cup squad was announced, with the player conveyed from the team's plane on arrival back in Dublin on Sunday afternoon to a private sports clinic, where the grim news was confirmed.

Healy is 35 but, along with vast experience, he still maintains a high standard in cameos as a replacement, while he can also play tighthead and scrummage as a hooker if needed.

More importantly, his class and composure offered comfort to a coaching team that has watched a hamstrung Dave Kilcoyne struggle for fitness in the warm-up schedule. The absence of Healy, the struggles of Kilcoyne and the inclusion of thrice-capped Jeremy Loughman all adds to the enormous burden on Andrew Porter not merely to stay fit, but also to play as long as he can in the Tests that count - most obviously, of course, against South Africa.

But how much one player, no matter how good, can endure when the opposition are replenishing almost their entire pack with a half to play, has to be questioned.

The same goes for Tadhg Furlong on the tighthead side. And that's before the awfully delicate matter of the health of the hookers is raised. It's a jolting pointer to the delicate margins that will end up deciding Ireland's World Cup outcomes.

And it is based not on what happened in Bayonne or a Dublin hotel at the weekend, but early in the second half of a South African rampage across London.