CTE, or Chronic Traumatic Encephalopathy, is commonly found in US footballers, and has now been found in 2 Australians who played NRL. Their identities are confidential.
Caused by repeated concussions and blows to the head, CTE exhibits symptoms akin to Alzheimer’s Disease, however, it is only with a post-mortem of the brain that CTE can definitively be proven.
https://www.news.com.au/sport/nrl/groundbreaking-discovery-in-nrl-brain-disease-crisis/news-story/d25518cecdd18a4c371ffd8935ad675b