The study was led by Patricia Conrod, of King's College London's Institute of Psychiatry, with the University of Montreal and Sainte-Justine University Hospital Center in Canada.

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Dr Scott Delaney, research director of emergency medicine at McGill University Health Center in Montreal, Canada, has also researched soccer-related head injury and agrees that head-to-head or elbow-to-head blows are the real risk.

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