Late Dallas Cowboys defensive end Marshaw Kneeland was diagnosed with chronic traumatic encephalopathy (CTE) after he died by suicide, aged 24, in November 2025, which was revealed through the test results, performed by the Concussion & CTE Foundation, released by his family.
Dr. Ann McKee, the Boston University CTE Center director and chief of neuropathology for the VA Boston Healthcare System, noted that the discovery aligned with research that covered athletes within a similar age range.
"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," McKee shared in her statement.
Results Have Shown a Pattern Among Young Athletes
CTE can currently only be diagnosed after death, through examination of brain tissue, and is staged from 1 (mildest) to 4 (most severe). Kneeland's CTE was determined to have been at Stage 1.
Stage 1 CTE has been associated with short-term memory problems, depression, aggression, impulsivity, and executive-function difficulties. Both BU and the Concussion & CTE Foundation stressed that suicide is complex and multifactorial, and that a CTE diagnosis is not established as a direct cause. Records reviewed by ESPN show mental health concerns had surfaced years earlier, dating back to 2020 at Western Michigan University.
Foundation CEO Chris Nowinski noted that Kneeland played during the era of modern concussion protocols and improved helmets, yet still developed the disease, which reinforces that current safety measures don't prevent CTE, since it's driven by cumulative, repeated head impacts rather than diagnosed concussions alone.
What Is CTE: A Closer Inspection
Chronic traumatic encephalopathy (CTE) is a progressive brain disease linked to repeated head impacts, identified in former football players, boxers, other high-contact sport athletes, and military veterans. This accumulated head trauma, including subconcussive impacts during contact sports, not just diagnosed concussions, has led researchers to believe that this results in a buildup of tau protein that damages brain tissue over time.
As of now, CTE can only be confirmed after death via brain tissue analysis; there's currently no validated way to diagnose it in the living, though researchers are looking for a way to do so and creating tests that remain to be validated.
The following stages of CTE have been described as follows:
- Stage 1 : Mild headaches and difficulty concentrating.
- Stage 2 : More severe depression, mood swings, behavioral outbursts.
- Stage 3 : Memory impairment, difficulty organizing and planning, impulsivity, aggression.
- Stage 4 : Dementia, profound memory loss, language difficulties, motor decline.
Some possible symptoms may include the following:
- Short-term memory problems
- Suicidal thoughts
- Headaches
- Depression
- Mood swings
- Aggression or impulsivity
- Executive-function difficulties (planning, organizing, multitasking)
- Language or speech difficulties (later stages)
- Motor decline or dementia (later stages)
Taking Note and Acting Quickly
The condition has been documented in athletes who died before 30, football players at all levels, boxers, and veterans, among others. It is noted that CTE has not been established as a direct cause of suicide, as suicide risk involves many overlapping factors, but remains important to monitor.
If you notice concerning symptoms like memory changes, depression, or aggression in yourself or someone else, these have many possible causes and are worth discussing with a doctor or mental health professional, who can properly evaluate what's going on. If there are thoughts of self-harm, contact the 988 Suicide & Crisis Lifeline immediately.
A Call for Change to Save the Coming Generations of Athletes
The case of Marshaw Kneeland adds to growing evidence about the long-term risks of contact sports, even for athletes competing under modern safety conditions. It indicates that helmets and concussion protocols, while valuable, aren't designed to address the cumulative, repetitive impacts researchers believe actually drive CTE. In turn, real prevention may require reducing head impacts at every level of the sport, not just managing concussions after they happen.
The former football player dying at 24, and being among athletes found to carry signs of the disease before 30, shows CTE isn't only a concern for players decades removed from their careers. His family's choice to share the diagnosis publicly reflects a broader shift away from the taboo around athlete mental health and brain injury, which is a shift researchers say is essential both for scientific progress and for athletes who may be quietly struggling.
