THE PACK: FORCES AT SCRUM TIME

The problem

Statistics indicate that almost half of serious spinal injuries in rugby occur during scrums. Research in South Africa (2011) shows that nearly all scrum-related injuries occur at impact – just over one-half the result of the engagement and approximately one-third resulting from subsequent scrum collapses.

Over the years, the IRB has amended scrum laws to try to reduce injuries. Canterbury commissioned Dr John Biggins, a physicist in the Theory of Condensed Matter Group at Cambridge University, to analyse the engagement and push forces in scrums during the 2013 Six Nations and the 2016 Six Nations to assess the effects of the changes.

Scrum law changes

Faced with the problem of massive, often dangerous, hits at engagement and players sometimes going to ground if they felt disadvantaged, which put player at risk and frustrated fans with the constant need to reset scrums. In 2007 the IRB introduced the ‘crouch, touch, pause, engage’ law to speed up scrums and ensure both sides were ready for the contact. Unfortunately, scrums still took a long time to set, the engagement was still a major collision because the packs were still too far apart and scrums still regularly collapsed.

Refinements have led to a ‘crouch, bind, set’ system for the 2016 Six Nations. The packs form on crouch; the props then loosely bind onto their opponents, ear to ear, and maintain the bind until the referee calls ”set”, when the packs engage.

The different rugby scrum forces explained with the 2013 and 2016 rules
Rugby scrum force reduction comparing 2013 and 2016

The findings of the scrum analysis

Dr. Biggins’ analysis shows that in 2013, the England pack (at 930kg, the heaviest and most powerful in the Six Nations) engaged at a velocity of 1.3 metres per second with a hit force of 16,500 Newtons (more than twice the 8,200 generated by the Scots) and a traction force of 9,100 Newtons for a total force of 25,600 Newtons, enough to lift a Land Rover.

The results for 2016, however, show dramatic decreases in impact velocity and hence hit force. France now has the highest impact velocity with 0.9 metres per second and the highest hit force at 6,900 Newtons. With a traction force of 8700 Newtons, this gives a total force of 15,600, just enough to lift a Volkswagen Golf.

While traction forces for all the nations are relatively unchanged (ranging from a high 8,900 Newtons for Ireland to a low 8,700 for all but England with 8,800), hit forces have been more than halved, close to 75% in some cases. England’s hit force is down to 3,500 Newtons and Scotland’s is a mere 800 Newtons.

Rugby Six Nations Scrum statistics of 2013
Rugby Six Nations Scrum statistics of 2016

A safer game

When translated into the affect on players, these results mean that, under the new rules, front rows are subjected to much lower impact forces and hence the risk of serious injury is considerably reduced, which is what all lovers of the game want to see.

About the research

The statistics produced in this report were produced by Cambridge University physicist, expert in Theoretical Condensed Matter Physics. 

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