Was Japan’s win a random event ? We think largely so.

We are all for upsets in RWC, but was Japan’s win vs Springboks a random event (i.e. not part of an explainable pattern) ?  Our empirical analysis, based on ESPNScrum.com data, suggests it probably was largely so, with several factors potentially explaining the Springboks sub-par showing.

Why ? Japan entered the tournament ranked 13, the Springboks 3.  During the pre-tournament period from 24th September 2013, Japan played against 12 other RWC 2015 participants.  Their win ratio was 63% (76% in all games played including non RWC sides).  Over that time though, they only played one world rugby power – a loss to New Zealand.  In four other attempts against higher ranked nations, they had one win – Samoa (rank 12).  That would not indicate a pattern of success against stronger sides.

A quick sense check: Japan’s ranking was based on World Ranking points of 72.06; South Africa’s was 85.15 – a gap of 13.09.  Japan has 107k registered rugby players, South Africa 342k.

So while caution is always necessary when working with small samples (representativeness problems with only a few games), it is not immediately obvious that Japan’s win was part of a wider pattern.

How to rationalise ? Well, it could be a pure one off random event (roll a dice six times, you can get six sixes – though not very often).  For explanations, one could also look to behavioural economics and the possibility of an over-confidence bias on South Africa’s part. Bear in mind also that the Springboks will look to challenge in the business end of the competition, so it may be that they were conserving energy; that combined with the effect of well documented pre-tournament Springbok injuries .

If that’s a struggle, ask the following question. If Japan played the Springboks 100 times under equivalent conditions, who would win ?  Their form suggests at best a win ratio of less than 63%.

In conclusion, the above neither diminishes the achievement (playing and coaching) – probably the opposite actually; nor the fan value of an upset (other than for Springbok fans of course). 

For more details, the first table below shows Japan’s overall results summary for the period.  The second focuses on RWC 2015 participants only (so stronger nations).

Overall Figures (All Opposition, Home and Away)
Span Mat Won Lost Win %
2013-2015 25 19 6 76.00
Versus Other RWC Participants      
Nation Mat Won Lost Win % World Ranking
New Zealand 1 0 1 0% 1
Fiji 1 0 1 0% 9
Scotland 1 0 1 0% 10
Tonga 1 0 1 0% 11
Samoa 1 1 0 100% 12
Italy 1 1 0 100% 14
USA 2 1 1 50% 15
Georgia 2 1 1 50% 16
Romania 1 1 0 100% 17
Canada 2 2 0 100% 18
Uruguay 2 2 0 100% 19
Russia 1 1 0 100% 22
Totals 16 10 6
Average 63%

Source: ESPNScrum.com, own calculations

World Rankings shown are pre-tournament.

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Empirical Rugby

Empirical Rugby is a blog that provides fundmental insight into rugby union using empirical analysis of rugby data.

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