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Ireland’s Joe McCarthy conundrum: can he do the business at the breakdown?

Saturday’s game will be the biggest test of the 23-year-old lock’s young international career

Ireland’s Joe McCarthy celebrates winning the Six Nations earlier this year. Photograph: Dan Sheridan/Inpho

It doesn’t take a genius to find a common thread to Ireland’s significant losses in the Andy Farrell era.

Sam Cane and Ardie Savea’s opening-quarter dominance of the breakdown haunted Ireland for weeks after their World Cup quarter-final defeat to the All Blacks. When England ended hopes of back-to-back Grand Slams earlier this year, they left Ireland with their highest rate of slow ball – rucks lasting longer than six seconds – of the entire Six Nations (22 per cent).

Six of the starting Irish pack on Saturday were part of the Leinster outfit which succumbed to a Toulouse defensive breakdown masterclass in the Champions Cup final. All told, with the likes of Jack Willis and Antoine Dupont running rampant, Leinster conceded 18 turnovers across the park.

Stop any side on the floor and they will struggle to win. Yet with Irish teams, given their reliance on dominating possession and taking defences through multiple intricate phases of attack, this basic tenet rings true for them more so than most. Despite this being one of the worst-kept secrets in rugby, statistically speaking at least, Andy Farrell has not picked his best pack when it comes to rucking to take on a South African team which is well equipped to go after the Irish breakdown.

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Here lies Ireland’s Joe McCarthy conundrum.

Saturday will be the biggest test of the 23-year-old lock’s young international career. When McCarthy was being interviewed by press during this year’s Six Nations, he was asked about the reasons for his success so far in the campaign. “Because he’s f**king massive!” came the supportive response from a passing team-mate who overheard the conversation.

His power both when carrying and tackling has been a revelation for an Irish side calling out for his sort of bulk in the secondrow. Now, for the first time, McCarthy finds himself squaring off against “f**king massive” lock royalty in the form of the Springboks with the likes of Eben Etzebeth and Franco Mostert in tow.

Joe McCarthy impressed for Ireland on his Six Nations debut against France earlier this year. Photograph: Shaun Botterill/Getty Images

McCarthy is comfortably Ireland’s best secondrow when it comes to carrying through heavy traffic, utilising his combination of size, footwork and all-round athleticism.

According to sports analytics company Opta, of Ireland’s three locks in the squad this weekend – McCarthy, Tadhg Beirne and James Ryan – “Big Joe” recorded the highest rate of dominant carries both in the recent Six Nations (20 per cent) and in this year’s domestic action (44 per cent). Sticking with domestic games for Leinster, a larger sample size, McCarthy was also the best Irish lock at breaking the gainline (61 per cent of carries) and at drawing in more than two defenders (77 per cent). As well as punching more holes, he is adept at leaving fewer would-be tacklers and therefore more space behind him for Ireland’s wide attack.

McCarthy also offers a significant grunt in defence. His dominant tackle rate of 14 per cent for his club and 10 per cent during the Six Nations are comfortably the highest figures among Ireland’s current back five forwards.

The rough that comes with this carrying smooth brings us back to the breakdown. Rough is probably a harsh word to use. McCarthy is by no means a bad breakdown operator. Yet it remains true that if Ireland wanted to pick their best pack for securing quality ruck ball, the numbers suggest McCarthy would not be starting.

In this year’s club action, of Ireland’s trio of locks, McCarthy is the least effective at clearing out rucks. Eighty-two per cent of his breakdown arrivals for Leinster this season, in URC and European action, have been positive. Ryan’s figure is 93 per cent, while Beirne’s is 94. Ryan is on the bench on Saturday. McCarthy starts alongside Beirne.

The issue is not work rate. In the 2024 Six Nations, McCarthy hit more attacking rucks (111) than Beirne (81), Josh van der Flier (99) and Peter O’Mahony (62). The Twitter account AnalystGus recently used Oval Insights figures to show that, with a rate of 25 attacking ruck arrivals per game, McCarthy’s fitness for such a high workload left him in the higher percentile of locks in the URC. These numbers, though, do not reflect the quality of such arrivals in the same way as the Opta data above.

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South Africa are world rugby’s disrupters-in-chief, in all facets of the game, but particularly the breakdown. Leinster players have added the word “s**tfight” to their rugby lexicon to describe their attitude to defensive rucks since Jacques Nienaber, the South African World Cup-winning coach, joined their ranks.

In advance of this Ireland tour, former Munster hooker Jerry Flannery joined the ‘Boks as defence coach, replacing Nienaber. Having worked with his predecessor when both were at Munster, Flannery has previously said that Nienaber was the best coach he worked with. When coaching at Harlequins, Flannery implemented a similar philosophy of blitzing outside backs and niggly forwards, causing havoc at the breakdown. Harlequins backrow Will Evans previously led the Premiership for turnovers forced per 80 minutes.

Given the stylistic similarities, Flannery is largely a continuity appointment who won’t radically overhaul the system devised by Nienaber. Come Saturday, South Africa will be s**tfighting aplenty.

They’re mighty good at it. When these two sides met at the World Cup, Ireland’s victory came despite South Africa slowing their average ruck speed down to their worst figure recorded at that tournament (4.8 seconds per ruck). This was one of a number of statistical categories that suggested South Africa were the better team on the day.

Lies, damned lies and the statistics that show Ireland should have lost to South AfricaOpens in new window ]

In Siya Kolisi, their captain and openside flanker, South Africa have a quality defensive operator. For Racing 92 this season, he slowed up opposition ball on a quarter of the rucks he hit, placing him inside the top 15 players globally for defenders who have seen 50-plus breakdowns. At last year’s World Cup, Kwagga Smith, who starts this weekend at number eight, slowed up 42 per cent of his defensive rucks. Granted, that last number is possibly inflated by Smith’s role as supersub allowing him to feast on tired attacking ruckers.

Farrell and his coaching staff had a decision to make between the value placed on the breakdown and the required extra grunt required when carrying and tackling against a mammoth Springbok team. This is not to say Ireland undervalue the breakdown. Globally, assistant coach Paul O’Connell is widely regarded as one of the best operators when it comes to detail at attacking rucks.

Regardless, by not picking the better attacking rucker in James Ryan, Ireland are employing a balancing act. Will that difference derail their attack? One player is unlikely to have that much influence. Perhaps the quality of Ireland’s other back five forwards makes such a balance easier to swallow. Beirne, O’Mahony, Caelan Doris and Van der Flier have all had a ruck success rate of over 90 per cent this year.

McCarthy will be a key part of Ireland’s bid to match South Africa’s power in attacking and defensive collisions. What happens in the trade-off between that and Ireland’s breakdown efficiency will be a similarly important factor influencing Saturday’s result.