Cowboys defensive lineman Marshawn Kneeland died by suicide in November 2025 at age 24. His family has released the results of a post-mortem brain tissue analysis performed by the Concussion & CTE Foundation.
Via a release from the Concussion & CTE Foundation, Boston University CTE Center researchers diagnosed Kneeland with stage 1 chronic traumatic encephalopathy (CTE).
Stage 1 is the lowest level, on a scale of 1 to 4.
“Unfortunately, I was not surprised to find CTE in the brain of Mr. Kneeland, because we have found this progressive brain disease in nearly half of the athletes we’ve studied who have died before the age of 30,” Dr. Ann McKee, director of the Boston University CTE Center, said. “Thanks to the generosity of our brain donor families, we now better understand the earliest stages of CTE, and it is bringing us closer than ever to diagnosing it during life. My team and I are fully dedicated to finding effective treatments and a cure for CTE.”
CTE still can be diagnosed only by studying the brain tissue of a patient who has died.
“Mr. Kneeland played in the modern era of concussion protocols and better helmets, and yet he still developed CTE,” Concussion & CTE Foundation CEO Chris 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.”
NFL players often say they know what they signed up for. It’s important that all players, at every level of the sport, realize that the risks of immediate and acute injury include the possibility of developing long-term problems, such as CTE, ALS, Alzheimer’s disease, and Parkinson’s disease.
“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,” Kneeland’s girlfriend, Catalina Mancera, said. “We share this information to help people understand what NFL and other high contact sport athletes might be struggling with. Raising awareness is important to us. We continue to remember Marshawn with compassion for the person he was, rather than defining him by the final moments of his life.”
And, no, it’s not just football. Anyone watching the World Cup has witnessed the repeated blows that soccer players embrace when they strike the ball with their head. It’s moving in one direction, and the players provide enough force to send it in another direction — often the opposite direction. That increases the total force of the blow, and headers are extremely common in the sport.
Hockey, rugby, and boxing and other combat sports result in blows to the head. Even basketball players suffer head trauma that is usually less than a concussion but still a blow to the skull — and to the brain inside it.
Most will accept the short- and long-term risks in exchange for the benefits of participating in sports, especially at the highest levels. Still, they all need to understand the full range of risks when deciding whether to do so.
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