The football world was shocked when retired former Denver Broncos wide receiver Demaryius Thomas died last year at age 33 after suffering a seizure, initially thought to be related to injuries from a 2019 auto accident. Now doctors know more about a key factor contributing to his death: In July, Thomas became the latest NFL player to be diagnosed posthumously with CTE. 

CTE – chronic traumatic encephalopathy – is a degenerative brain disease that has been linked to recurring hits to the head and episodes of concussion, which are common in football and other contact sports.

A major challenge dealing with CTE is it can only be diagnosed postmortem, meaning it is left untreated and can lead to player’s death at a young age. One study found that the brains of 110 out of 111 former NFL players showed signs of CTE when autopsied.

To compile a list of 35 professional football players whose deaths are at least partially attributable to CTE, 24/7 Tempo reviewed profiles of players published by the Concussion Legacy Foundation and articles published by Boston University’s CTE Center. We also reviewed archived news stories about deceased football players published on ESPN, CNN, Sports Illustrated, NPR, and other online sources.

Click here to see a list of famous football players known to have had CTE

Some of the most common symptoms of CTE are confusion, impaired judgment, and severe mood swings that often include aggressive responses. Several of the former football players on the list have had a history of violent behavior. (These are 33 athletes with famously bad tempers.)

In some cases, the violence goes to the extreme. For instance, in 2015, New England Patriots tight end Aaron Hernandez was found guilty of the 2012 murder of semi-pro linebacker Odin Lloyd and later died in prison, an apparent suicide; and last year, cornerback Phillip Adams, who’d played for numerous NFL teams, shot six people before turning the gun on himself.

In recent years, suicide has been widely cited as being associated with CTE. Of the 35 men on the list, at least 12 have died by their own hand. (These are 37 violent celebrity deaths.)