Marshawn Kneeland, a former Dallas Cowboys defensive end who died by suicide in November 2025 at the age of 24 following a high-speed police chase, has been posthumously diagnosed with early-stage chronic traumatic encephalopathy (CTE). The finding matters because it adds a young NFL player to the growing body of evidence linking repetitive head impacts in contact sports to degenerative brain disease, and because it offers his family and the public possible context for the struggles he may have faced before his death.

The diagnosis, Stage 1 on a four-stage scale where Stage 4 indicates the most damage, was made by the Boston University CTE Center from postmortem brain tissue, and the results were released by his family through the Concussion & CTE Foundation. His family, including his girlfriend Catalina Mancera, said they shared the results to raise awareness of what athletes in high-contact sports may endure. Dr Ann McKee, who directs the centre, said she was unsurprised, noting CTE has been found in nearly half of the athletes her team has studied who died before the age of 30.