1905–1906
After 18 player deaths, President Theodore Roosevelt pushes for college football reform. Teams agree to adopt the forward pass, a safer way to move the ball.
- 1910
New college rules outlaw interlocking interference and the deadly "flying tackle."
1943
NFL players are required to wear headgear. 
1949
The plastic helmet is legalized, replacing leather. Critics say the hard shell allows players to use their heads as weapons.- 1955
The single-bar face mask becomes the NFL standard.
1976
After years of spinal injuries, the NFL bans the head-on spear tackle. - 1978–1980
Greater penalties are placed on head and neck contact.
- November 2003
A University of North Carolina study links multiple concussions with a threefold increase in depression. The co-chairs of the NFL's Mild Traumatic Brain Injury (MTBI) Committee deny the study's credibility.
2004
The NFL outlaws the single-bar face mask, stating that it doesn't offer enough protection.- July 2005
Researchers at the University of Pittsburgh publish the first finding of chronic traumatic encephalopathy (CTE) in an NFL player's brain. The NFL demands a retraction. - October 2006
Former professional wrestler and Harvard football player Christopher Nowinski publishes Head Games: Football's Concussion Crisis from the NFL to Youth Leagues. 
- March 2007
The head of the NFL's MTBI Committee leaves his post amid controversy over his lack of appropriate medical credentials. - March 2007
The league establishes the 88 Plan, which provides funds for former players struggling with Alzheimer's disease and dementia.
- May 2007
NFL commissioner Roger Goodell announces mandatory neuropsychological testing for all players and a "whistle-blower system" to report coaches who force concussed players to return to the field.
- June 2007
NFL convenes concussion summit for team doctors and trainers. Cochair of the MTBI Committee says CTE has never been scientifically documented in football players. - August 2007
NFL mandates that teams should not put players who have been unconscious back in a game or practice.
September 2008
BU School of Medicine and the Sports Legacy Institute found the Center for the Study of Traumatic Encephalopathy (CSTE).- September 2008
CSTE announces its finding of CTE in the brain of former player John Grimsley. A dozen athletes, including six NFL players, agree to donate their brains to the center.
January 2009
CSTE announces two new cases of brain degeneration in deceased players, including one high school athlete who was only 18 years old.
- October 2009
Results of an NFL-commissioned study are leaked. They show a significantly higher incidence of Alzheimer's, dementia, and other memory-related diseases among former NFL players. 
October 2009
The U.S. House of Representatives Judiciary Committee holds hearings to examine the NFL's alleged neglect of former players with brain injuries.
November 2009
NFL agrees to require independent neurologists, rather than league doctors, to treat players with brain injuries.
- November 2009
NFL, along with the U.S. Centers for Disease Control and Prevention, broadcasts public service announcements warning youth of the dangers of head trauma.
December 2009
NFL publicly states its intent to give CSTE
$1 million to fund its research.- February 2010
Eighteen more former and active NFL players agree to donate their brains to CSTE. They join 250 other athletes, 60 from the NFL. 
March 2010
The NFL replaces the MTBI Committee with the Head, Neck and Spine Medical Committee, effectively disbanding the MTBI and abandoning its research.
- March 2010
CSTE codirector Robert Cantu is senior advisor to the new committee, which includes some of the NFL's harshest critics.
April 2010
NFL donates $1 million in unrestricted support to BU's CSTE. 
May 2010
NFL commissioner Goodell sends a letter to all U.S. governors urging them to pass youth concussion legislation.- July 2010
NFL produces locker room posters that spell out the dangers of concussions and brain damage. The posters remind players that "younger athletes are watching."
- August 2010
Boston University researchers link sports-related head injuries to a newfound ALS-like disease. 