Scrum Science: Rugby Union Scrummaging by the Numbers

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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 Science 1Every 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 N +/- 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!

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.

Scrum Science 2

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




For a heavily American-ised version of this article I suggest the following ESPN Sport Science. Apparently they could only get there hands on Rugby Union footage from the 1980s. I also spotted a few Rugby League clips that had somehow found their way into the footage.

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