The players the Springboks simply cannot be without for the British & Irish Lions tour

In the two-year run-up to the Springboks' World Cup victory, the side perfected and mastered a high-risk, high-energy defensive system under Rassie Erasmus and defence coach Jacques Nienaber.

Precariously placed heading into South Africa's away game in Wellington back in 2018, Rassie Erasmus claimed he was under pressure and would quit if they lost, citing his record of never losing three matches in a row as a reason.

Their defence gave up 34 points in a wild and thrilling narrow victory, but it was that aggressive defensive system that came through to pressure Damian McKenzie into dropping the ball on the very last play to seal the win.

It wasn’t perfect, but it worked when it mattered.

In the return match in Pretoria, a dominant showing had the All Blacks completely powerless for the first time in a long time, with the visitors tryless for the first 54 minutes.

At 30-13 after an hour’s play, a serious warning light was flashing.

Not since before the 2015 World Cup had an All Black side been so thoroughly outclassed and out of answers. The reigning world champions and pioneers of try-scoring rugby were flummoxed, down heavily in a test match for the first time since 2012 at Twickenham.

Even the loss the year prior at home to the Lions with 14-men on the park had the All Blacks leading heading into the last quarter of the game.

A calamitous last twenty minutes by the Springboks handed the game away and the first 60-minutes of the game was quickly forgotten.

It shouldn’t have been, as it was the first real sign that the Springboks were in the process of developing the world’s best defence.

The Springboks continued to tinker and made changes to find the best formula.

Lukhanyo Am became the starting centre and Jesse Kriel became the finisher. Two starting quality centres, 1a and 1b, used in tandem to bring endless amounts of pressure.

With Am going off after 50 minutes, a fresh Kriel could come on and charge off the line for the remainder of the game, continuing the suffocating pressure needed to stop the ball ever getting to the edge.

In order for this system to work, it requires supremely conditioned athletes on the fringes.

Having one tank of fuel for each half meant that the energy would never dip out wide with one centre replaced by the other.

This means that Jesse Kriel is as important to the Springboks’ defence as Lukhanyo Am. The likelihood either one of them could keep up consistent intensity by themselves for the full 80 is unknown.

Certainly they would aspire to, but it would be a superhuman effort to actually do so.

The issue ahead of the Lions tour is the Japan Top League is not the ideal preparation for the physicality of test rugby, where Jesse Kriel currently is playing.

With only a handful of teams at a Super Rugby level, there isn’t consistent competition each and every week.

At 26-years-old, he is certainly not done in the test arena, but a question mark resides over whether Rassie Erasmus will pick Springboks out of the Japanese competition.

Erasmus says Europe is comparable to Test rugby, but the Top League is definitely not.

Outside centre options in South Africa not named Lukhanyo Am are lacking.

The Bulls last used Tongan-international Nafi Tuitavake. Ruhan Nel of the Stormers is a career Sevens player. Graduate South African under-20 prospect Mannie Rass of the Lions is promising but rather unproven as yet.

Jesse Kriel coming back to South Africa or finding a club in Europe is just what the Springboks need, otherwise Nienaber’s defensive system will suffer, with Am required to play high-intensity defence for eighty minutes.

The end of year tour in 2018 also gave Rassie Erasmus a taste of life without Faf de Klerk.

They beat Scotland narrowly and lost to Wales and England. The halfback options didn’t light the world on fire until Herschel Jantjies burst onto the scene in 2019 to become the reserve halfback.

As good as Jantjies has shown so far, there just isn’t another halfback in World Rugby that can do what de Klerk does in defence and a Springbok side starting Jantjies would be vastly different.

De Klerk can handle any winger one-on-one, shut down overlaps even when outnumbered, and his defensive spatial coverage across the pitch is second to none. His GPS numbers must be off the charts.

He knows when to shoot up and take space, when to commit to the tackle and when to hold off. He plays as an edge defender, a sweeper and a front line defender in the middle all in one.

Not to mention his physicality in contact; no other halfback comes close except perhaps Antoine DuPont.

His role in the defence is basically the glue that holds it together, often the last man in the chain to prevent the opposition from breaking away. And he does this time and time against the odds.

Without him, the entire defensive system risks falling part and the Lions' chances of winning in South Africa dramatically increase.

Then there's Cheslin Kolbe.

Kolbe has the most dangerous feet in the world. But that’s not the only reason why he became the first choice right winger under Erasmus.

Much like Am and Kriel’s ability to make the right decision when jamming in, Kolbe’s edge defence is spectactular. His reads and decisions are consistently excellent, and his tackle completion percentage is high.

South Africa’s number two right-wing, Sbu Nkosi, was beaten multiple times by Wales in the opening twenty minutes of the World Cup semi-final, caught out in no man's land as the Welsh continually raided the left-hand channel.

Wales' one try of the match came through Josh Adams with centre Jonathan Davies gifting him the last pass off a scrum play. Nkosi was out of sync with Am on the blitz, arriving too late to shut down the play.

If Davies is lining up for the Lions next year, the Welsh centre will be licking his lips if he sees Nkosi out wide.

Whilst the Springbok pack is vitally important to their set-piece and physicality in close, what really keeps the opposition score surpressed is the work of the Springbok centres/wings and halfback out wide in Neinaber's system.

The Lions rolled out a successful width attack around the Sexton/Farrell axis in New Zealand in 2017. If they bring a similar plan, it puts these three guys under the microscope who have been absolutely critical to making the Springboks a historically great defensive side.

A Springbok side minus De Klerk, Kolbe or either Am or Kriel would be a very enticing opponent for Warren Gatland.