A degenerative brain disease that has been linked to concussions and other head trauma common in military combat and contact sports, CTE 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.

Mayor Eric Adams told MSNBC the gunman referenced CTE, a disease linked to head trauma, in a note before killing four people at 345 Park Ave., which houses the NFL.