A concussion expert told British lawmakers on Tuesday that football's management of head injuries was a "shambles" at the beginning of a parliamentary inquiry into the issue.
Consultant neuropathologist Willie Stewart was speaking to MPs on the House of Commons Digital, Culture, Media and Sport committee.
A 2019 study led by Stewart found that professional footballers were three-and-a-half times more likely to die from neurodegenerative disease compared with members of the general population.
He also examined the brain of English World Cup winner Nobby Stiles following his death in October and concluded that Stiles had been suffering from CTE (chronic traumatic encephalopathy), which is only found in people with a history of repetitive head trauma.
Football's lawmakers, the International Football Association Board, have approved trials of permanent concussion substitutes and the Premier League is experimenting with the new rule.
But Stewart criticised football's approach, saying it should have followed rugby's model, in which temporary substitutes come on while a player's head injury is assessed.
"Football has a habit, whenever it is forced to develop, of going out on their own and trying to develop something unique to everybody else as if the problem never occurred before," he said.
"What football has introduced is a shambles in 2021."
Asked whether temporary substitutions were preferable, Stewart added: "Unquestionably. Rugby has made great developments in understanding how you can assess and identify players with brain injury on the field, and that should be the model and the benchmark that (other) sports start from.
"They shouldn't be starting with a blank page and drawing up a protocol, they should just be saying 'how do we make that happen in football?'"
Rugby is also wrestling with the issue of head injuries.
A group of former professional players, including England's World Cup-winning hooker Steve Thompson, are involved in a legal case against a number of governing bodies after being diagnosed with neurological conditions.
Stewart said rugby could be made safer even though it was a contact and collision sport.
"I know a lot of people who work within rugby at a national and international level on the medical side and the performance side who are wrestling with this issue," he said.
"On the one hand, the global business, the industry, there is a revelling in the collisions and the contact, but it's doing a lot of damage to young men and women so they are desperately trying to find a solution."
Stewart said head impacts were probably leading to long-lasting brain injuries in athletes across a range of sports but that it would be a "virtual impossibility" to prove it beyond reasonable doubt.
"We take the position that the only thing that connects football to American football to boxing to rugby to wrestling to other sports where we have seen this pathology is head impact and head injury exposure," he said.
"There must be something else because people can have exposure to head injury, people can play the sport the same way and don't develop problems, there must be other things contributing to it, but the one common factor is this head injury.
"To prove it beyond a reasonable doubt as opposed to on the balance of probabilities is a virtual impossibility because the exposure is in their 20s and the outcome is 30, 40 years later."
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