Former Dallas Cowboys defensive end Marshawn Kneeland, who died by suicide in November 2025 after a high-speed chase with police, had early stage chronic traumatic encephalopathy (CTE), a brain abnormality linked to repeated concussions, his family announced Tuesday.

CTE Diagnosis

The Boston University CTE Center, which investigates the long-term consequences of repetitive brain trauma in athletes and others, analyzed Kneeland’s brain tissue after his death. Researchers determined Kneeland, who was 24, was in stage one of four of CTE.

CTE is a degenerative brain disease that has been found in athletes in contact sports, combat veterans and others who experience repetitive head trauma. It has been known to cause violent mood swings, impulsive behavior and depression. It can be diagnosed only after death.

Kneeland’s family, including his girlfriend, Catalina Mancera, said in a statement issued through the Concussion and CTE Foundation, “While this diagnosis does not change the tragedy of his passing, it provides important context about some of the struggles he may have been facing. We share this information to help people understand what NFL and other high contact sport athletes might be struggling with.”

Dr. Chris Nowinski, CEO of the Concussion & CTE Foundation, noted Kneeland’s diagnosis comes even amid a modern era of concussion protocols in professional and college athletics and better safety equipment.

Kneeland started playing tackle football when he was 7 years old. He played at Western Michigan University before he was selected by the Cowboys in the second round of the 2024 NFL draft.

Prevention and Awareness

Nowinski said, “We have no reason to believe the current generation is at a lower risk of CTE than previous generations. Concussion protocols do not prevent CTE, because CTE is caused by repeated head impacts, not just concussions. If we want to reduce CTE risk, we must implement CTE prevention protocols and aggressively reduce the number and strength of head impacts at every level of the game.”

Original reporting: Oklahoma City News Feed (HLL/CB) — read the source article.