10 Feb 2013

Scrum Science: Rugby Union Scrummaging by the Numbers

Having only ever played as a scrumhalf and fly half, I have always wondered what goes on in scrums. It is the real mystery in the game of Rugby Union. And I know that I am not alone when even the professionals are consistently confused by scrum penalties (a topic for another day maybe).

The set scrum, which was initially a means of restarting play after minor rule infringements, has become an integral part of the battle for physical and psychological supremacy over the opposition.

Scrum Machine with SensorsEvery year we see law changes designed to make the scrum safer. I want to understand the 'science of the scrum' & why it is so dangerous in the first place.

The scrum science numbers below are summarised from a New Zealand study of professional provincial Rugby Union forwards.

Scrummaging forces were measured in this study using strain gauges fitted to the shoulder pads of a purpose built scrummaging machine. The average pack impact force at the hit in professional scrummaging is 10,850 ± 1170 N.

If you are anything like me, that doesn't mean much. To put this in perspective, a knockout punch delivers some 3,000 N. That is 1/3 of the the force in the scrum!

Scrum Science forces in the scrum

While more injuries are sustained in tackles, the high forces on the exposed cervical spine (neck) mean that scrummaging injuries are more dangerous. And this is why ESPN calls the Rugby scrum the ‘historically the most dangerous moment in sport’.

Is it all in the Front Row?

It is also interesting to learn who is contributing what to the scrum. In a separate article on the Biomechanics of Scrummaging, Milburn reported that the three members of the front row produced 38% of the forward force generated by the entire pack, the locks produced 42% and the loose-forwards 20%. The low force contributed to the total scrum by the loose forwards is attributed to the body alignment of the players when scrummaging, with the props and locks transmitting force directly forward, whereas the flankers push into the scrum at an angle. This might also be linked to a strength differential between the positions.

Contribution to the Scrum by Position

Does size matter?

Interestingly, teams composed of stronger individuals did not always produce more force than those containing weaker individuals. After the hit, the mean impact force that packs were able to exert was 66% of the sum of their individual forces. These findings emphasize the importance of technique and coordination among the members of the scrum pack to enable them to produce force effectively.

This would explain why smaller teams can still compete at the scrum.

Cameron West
Cameron is the Director of Pro Training Programs


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  13. This is an awesome blog that people should definitely be keeping up on. I think more research needs to be done on the scrums in rugby. No one really knows the lasting impacts on the scrum and how important form in for all members of the scrum especially those binding. Keep up the relevant posts, much appreciated.

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  15. Really nice post here. I don't think too many people know just how much force is truly in the scrum, especially the front rows. I wonder what people think about the force to head and the concussion rate in collapsing scrums. I would be interested to hear some other opinions.

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