Billy Guyton, the former Blues and Maori All Blacks scrum-half, tragically passed away in 2023 due to a brain injury likely caused by repeated head knocks. He was the first professional rugby union player to be diagnosed with Chronic Traumatic Encephalopathy (CTE). Aside from playing for the Blues, Guyton also had stints with the Crusaders and Hurricanes in Super Rugby, as well as Tasman and North Otago in New Zealand's National Provincial Championship. He was 33 years old at the time of his death.

Guyton's brain was donated to the brain bank at the University of Auckland, where it was diagnosed with Stage Two CTE after comprehensive testing. His death was suspected to be by suicide in Nelson last May. Despite years of struggling and seeking help, his family only realized the extent of his condition after his passing. New Zealand Rugby expressed condolences to Guyton's family and acknowledged the concerning diagnosis. They emphasized the potential link between repeated head injuries in rugby and neurodegenerative diseases later in life.

Requested by Guyton's family, his brain was examined by a pathologist who confirmed the presence of CTE. Stage Two CTE, characterized by tau protein buildup in the brain's crevices, was found in Guyton's brain. The risk factors for CTE are limited, with head trauma being a significant contributor. Unfortunately, Guyton experienced multiple concussions during his playing career and was forced to retire in 2018 at the age of 28 due to debilitating symptoms.