The brain of former Dallas Cowboys defensive end Marshawn Kneeland showed evidence of Stage 1 chronic traumatic encephalopathy (CTE), according to researchers at Boston University’s CTE Centre, adding another sobering chapter to the sport’s long-running examination of repetitive head trauma.

Kneeland died on November 6th, 2025, from a self-inflicted gunshot wound following a police pursuit in Frisco, Texas. The diagnosis was announced Tuesday by the Concussion & CTE Foundation following a posthumous examination of the 24-year old’s brain tissue conducted by researchers at Boston University.

CTE Centre director, Dr Ann McKee, said that the diagnosis, while tragic, reflected a pattern researchers are increasingly seeing in younger athletes exposed to years of repetitive head impacts.

“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 revealed in an official statement.

Stage 1 represents the earliest of the disease’s four recognised stages. According to researchers, symptoms can include headaches, impaired concentration, short-term memory difficulties and mood changes, although the severity and presentation vary widely between individuals. Crucially, however, CTE can only be definitively diagnosed after death through examination of brain tissue.

Kneeland’s family said that, while the findings provide context, they could not furnish an explanation for the tragedy.

“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,” they confirmed. “We continue to remember Marshawn with compassion for the person he was, rather than defining him by the final moments of his life.”

In a separate statement released through the Concussion & CTE Foundation, the family added that they were prepared to ‘share this information to help people understand what NFL and other high-contact sport athletes might be struggling with’.

The CTE Centre also emphasised that CTE is not known to be a direct risk factor for suicide, noting that the causes of self-inflicted deaths are complex and multifactorial, prompting researchers to caution against drawing a direct causal link between Kneeland’s diagnosis and his death.

Chris Nowinski, co-founder and chief executive of the Concussion & CTE Foundation, argued the case demonstrates that advances in player safety have not eliminated the underlying risks associated with repeated head impacts.

“Mr Kneeland played in the modern era of concussion protocols and better helmets, and yet he still developed CTE,” Nowinski explained. “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.”

A second-round selection by Dallas in the 2024 NFL Draft out of Western Michigan, Kneeland appeared in 18 games for the Cowboys across two seasons, making four starts before his death.

The diagnosis also arrives just months after Boston University announced that Chicago Bears legend Steve McMichael had been found to have Stage 3 CTE following his death in April from complications of amyotrophic lateral sclerosis (ALS), the degenerative disease recently connected to former Titan Chris Johnson. Researchers continue to investigate possible links between repeated head trauma, CTE and certain neurodegenerative diseases, although many questions remain unanswered.

Boston University’s research remains one of the largest collections of posthumous brain studies involving former football players. In 2023, the CTE Centre reported finding evidence of the disease in 345 of the 376 former NFL players whose brains had been donated for research. Scientists have consistently cautioned that those figures should not be interpreted as representing the prevalence of CTE across all former NFL players because the brains are donated voluntarily rather than selected through a random population sample.