According to the Mayo Clinic, CTE — or chronic traumatic encephalopathy — is a brain disease most likely caused by repeated head injuries that damage the brain's nerve cells. The Mayo Clinic notes the only way to tell for sure if someone suffered from CTE is by autopsy.

The disease has been diagnosed in more than 100 former NFL players and arisen as an existential threat to the United States’ most powerful pro sports league.

Chronic traumatic encephalopathy, or CTE, is a brain disease linked to repeated hits to the head, often seen in military veterans and athletes.