Rugby World Cup: Pool B permutations for Ireland are simple if they beat Scotland. But, if they lose. . .

South Africa’s bonus-point win over Tonga has, as expected, taken them to the top of Pool B on 15 points after completing their four games, although their 49-18 winning margin means they have not overtaken Ireland’s points difference.

Hence, going into Saturday’s pool finale against Scotland, any two from three can still advance to the knock-out stages. But one bonus point could be sufficient for Ireland to top the pool and advance.

In the event of two sides finishing level on points, their final standings are decided by the head-to-head result. However, if there is a three-way tie, overall points difference decides first place, with second and third coming down to the head-to-head record.

Hence, while a win, draw or two bonus points would secure safe passage to the quarter-finals as Pool B winners, one losing point might now be sufficient for Ireland to progress to the last eight, provided they lost by four points or less, as they’d have the best points differential of the three.

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Ireland’s possibilities:

What happens if Ireland take zero points from next Saturday’s game?

If Ireland take nothing from next Saturday’s game, they will go out of the World Cup despite their epic win over the reigning world champions. A defeat without a bonus point would leave them on 14 points, meaning Scotland would join South Africa in the quarter-finals by dint of their head-to-head record against Ireland. So Scotland know that their minimum requirement is a win over Ireland by more than seven points

What happens if Ireland take one point from next Saturday’s game?

A solitary bonus point would secure Ireland a place in the quarter-finals provided they prevented Scotland from securing a try scoring bonus point, as this would leave them and South Africa on 15 points, with Scotland third in the final standings on 14 points. Ireland would also top Pool B ahead of South Africa by dint of their win over the Springboks.

However, one bonus point could suffice if Scotland won and scored four tries or more. In that scenario, all three sides would finish on 15 points, and curiously the tournament rules decree that first place would be decided by overall points difference in the group, while second and third would be decided by the head-to-head result.

So if Ireland lost against Scotland by five points or less, they would top the pool on points difference, and South Africa would qualify ahead of Scotland by dint of their head-to-head result. A defeat by six or seven points would see Ireland miss out.

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What happens if Ireland take two points or more from next Saturday’s game?

Two match points or more – ie a draw, two bonus points or a win of any hue next Saturday – would guarantee that Ireland advance to the knock-out stages as Pool B winners, as that would take them to 16 points and above both South Africa, who would qualify in second place, and Scotland, who would go out.