Marshawn Kneeland, a Dallas Cowboys defensive lineman who died by suicide in November 2025 aged 24, has been posthumously diagnosed with stage 1 chronic traumatic encephalopathy (CTE), researchers at Boston University's CTE Center have said. The finding matters because it adds to mounting evidence that the degenerative brain disease, caused by repeated blows to the head, is affecting American football players from a young age, even those who played under modern concussion protocols and with improved helmets.

CTE, which can only be diagnosed after death, was found via postmortem brain tissue analysis. Stage 1 is the mildest of its four stages, typically involving headaches and difficulties with attention and concentration, though later stages can bring depression, mood swings and suicidal thoughts. Kneeland's family said the diagnosis offered "important context" about his struggles and urged compassion. The centre's director, Dr Ann McKee, said CTE has been found in nearly half of the athletes studied who died before 30, while the Boston University centre previously diagnosed it in 345 of 376 former NFL players examined. The NFL has agreed a $1bn (£700m) settlement with more than 5,000 former players who sued it. Researchers stressed that the causes of suicide are complex and CTE is not a known risk factor.