(CNN) Here's some background information about concussions in the National Football League. A concussion is a type of traumatic brain injury caused by a blow to the head.
Reports show an increasing number of retired NFL players who have suffered concussions have developed memory and cognitive issues such as dementia, Alzheimer's, depression and chronic traumatic encephalopathy (CTE).
Most concussions occur without losing consciousness.
CTE is a degenerative disease of the brain and is associated with repeated head traumas like concussions.
Among the plaintiffs in concussion-related lawsuits: Art Monk, Tony Dorsett, Jim McMahon and Jamal Anderson.
(The NFL Player Concussion Pamphlet)
Loss of consciousness
(NFL - IQVIA)
(Preseason and regular-season practices plus games)
2012 - 261
2013 - 229
2014 - 206
2015 - 275
2016 - 243
2017 - 281
2018 - 214
2019 - 224
2020 - 172 (no preseason games due to the Covid-19 pandemic)
1994 - NFL Commissioner Paul Tagliabue creates the Mild Traumatic Brain Injury Committee. Dr. Elliot Pellman is named chairman despite not having experience with brain injuries.
2002 - Dr. Bennet Omalu, a forensic pathologist and co-founder of the Brain Injury Research Institute, identifies CTE in the brain of former Pittsburgh Steelers' center Mike Webster, 50, who committed suicide. Omalu is the first to identify CTE in American football players.
January 2005 - The NFL's Mild Traumatic Brain Injury Committee finds that returning to play after sustaining a concussion "does not involve significant risk of a second injury either in the same game or during the season."
2005 and 2006 - Dr. Omalu identifies CTE in the brains of former Pittsburgh Steelers players Terry Long and Andre Waters. Both had died by suicide.
February 2007 - Dr. Pellman steps down as chairman of the Mild Traumatic Brain Injury Committee but remains a member.
June 2007 - The NFL holds a medical conference on concussions.
August 14, 2007 - The NFL formalizes new concussion guidelines which include a telephone hotline to report when a player is being forced to play contrary to medical advice.
October 28, 2009 - Part I of the House Judiciary Committee hearing on Legal Issues Relating to Football Head Injuries. NFL Commissioner Roger Goodell defends the League's policy regarding concussions.
January 4, 2010 - Part II of the House Judiciary Committee hearing on Legal Issues Relating to Football Head Injuries. Dr. Ira Casson, one of the co-chairs of the Mild Traumatic Brain Injury Committee, denies a link between repeat head impacts and long-term brain damage.
March 2010 - The NFL's Mild Traumatic Brain Injury Committee is renamed the Head, Neck and Spine Committee. Two new co-chairs are selected, and Dr. Pellman is no longer a member of the panel.
October 20, 2010 - NFL Commissioner Goodell issues a memo to all 32 teams that warns of possible suspensions for offenders that violate the "playing rules that unreasonably put the safety of another player in jeopardy have no place in the game, and that is especially true in the case of hits to the head and neck."
February 17, 2011 - Former Chicago Bears defensive back Dave Duerson, 50, kills himself with a gunshot wound to the chest rather than his head so his brain can be researched for CTE. Boston University researchers find CTE in Duerson's brain, the same disease found in other deceased NFL players.
April 19, 2012 - Former Atlanta Falcons safety Ray Easterling, 62, dies by suicide. An autopsy finds signs of CTE. Easterling had been a plaintiff in a class action lawsuit against the NFL over concussion-related injuries filed in August 2011.
May 2, 2012 - Former NFL linebacker Junior Seau, 43, is found dead with a gunshot wound to the chest, classified as a suicide. Friends and family members say his suicide was brought on by multiple concussions, but an initial autopsy report finds no apparent brain damage. Portions of Seau's brain have been sent to the National Institutes of Health (NIH) for further study.
June 7, 2012 - A unified lawsuit combining more than 80 concussion-related lawsuits on behalf of more than 2,000 National Football League players is filed in federal court in Philadelphia. The players accuse the NFL of negligence and failing to notify players of the link between concussions and brain injuries, in Multi-District Litigation Case No. 2323.
August 30, 2012 - The NFL files a motion to dismiss the concussion related lawsuits filed by former players.
September 5, 2012 - The Foundation for the National Institutes of Health announces the NFL has committed to donating $30 million to support research on medical conditions prominent in athletes.
January 10, 2013 - The NIH releases the results of their analysis of Junior Seau's brain tissue confirming that Seau did suffer from CTE.
January 23, 2013 - Seau's family files a wrongful death lawsuit against the NFL, claiming that Seau's suicide was the result of a brain disease caused by violent hits he endured while playing the game.
August 29, 2013 - The NFL and ex-players reach a deal in the class action lawsuit that calls for the NFL to pay $765 million to fund medical exams, concussion-related compensation, medical research for retired NFL players and their families, and litigation expenses, according to a court document filed in US District Court in Philadelphia. The agreement still needs to be approved by the judge assigned to the case, which has grown to include more than 4,500 plaintiffs.
December 13, 2013 - The body of former NFL linebacker Jovan Belcher is exhumed in order to perform tests on his brain, a lawyer for the player's family tells the Kansas City Star. On December 1, 2012, Belcher, 25, shot his longtime girlfriend to death and then killed himself.
January 14, 2014 - A federal judge declines to approve a proposed $765 million settlement of claims arising from concussions suffered by NFL players, saying she didn't believe sufficient evidence had been produced to show that the settlement was adequate.
May 28, 2014 - Former Miami Dolphins quarterback Dan Marino and 14 other former NFL players sue the NFL over concussions. Their lawsuit claims the NFL knew for years of the link between concussions and long-term health problems.
June 3, 2014 - It is reported that Marino has withdrawn his name from the concussion lawsuit.
July 7, 2014 - The US District Court in Philadelphia grants preliminary approval to a settlement between retired NFL players and the NFL.
July 17, 2014 - Former NFL players Christian Ballard and Gregory Westbrooks file suit against the NFL Players Association, alleging the union withheld information about head injuries.
September 30, 2014 - Dr. Piotr Kozlowski releases a report on former NFL linebacker Belcher, stating that he likely had CTE when he killed his girlfriend and himself in 2012.
April 22, 2015 - A federal judge gives final approval to a class-action lawsuit settlement between the National Football League and thousands of former players. The agreement provides up to $5 million per retired player for serious medical conditions associated with repeated head trauma.
November 25, 2015 - Frank Gifford's family says he suffered from CTE. Gifford's diagnosis comes amid a growing focus on the risks athletes face from suffering repeated concussions, and just hours after the NFL admitted its concussion protocols had failed when St. Louis Rams quarterback Case Keenum kept playing Sunday even after his head injury on the field.
February 3, 2016 - Former Oakland Raiders quarterback Ken Stabler, who died in July 2015 of colon cancer, is diagnosed posthumously with CTE by researchers at Boston University.
March 14, 2016 - For the first time, a senior NFL official publicly acknowledges a connection between football and CTE. At a round-table discussion with the US House Committee on Energy and Commerce, when asked if "there is a link between football and degenerative brain disorders like CTE," Jeff Miller, the NFL's senior vice president of health and safety policy, answers "the answer to that question is certainly, yes."
July 25, 2016 - The NFL and NFL Players' Association (NFLPA) implement a new policy to enforce concussion protocol. Teams violating the policy are subject to discipline, through fines or losing upcoming draft picks.
September 14, 2016 - Commissioner Goodell announces an initiative intended to increase the safety of the game, specifically by preventing, diagnosing and treating head injuries. As part of the initiative, the league and its 32 club owners will provide $100 million in support of engineering advancements and medical research -- in addition to the $100 million previously pledged by the league to medical and neuroscience research.
July 25, 2017 - A study published in the medical journal JAMA identifies CTE in 99% of deceased NFL players' brains that were donated to scientific research -- 110 out of 111 former NFL players.
September 21, 2017 - Attorney Jose Baez tells reporters that results from tests performed on the brain of Aaron Hernandez, the former New England Patriots tight end who was convicted in 2015 of murder, showed a "severe case" of CTE. (The conviction was vacated after Hernandez's death in April 2017.)
November 10, 2017 - Researchers publish in the journal Neurosurgery, what they say is the first case of a living person identified with CTE. Lead author Dr. Omalu confirms to CNN that the subject of the case, while unnamed in the study, was former NFL player, Fred McNeill -- who died in 2015. The only way to definitively diagnose CTE is with a brain exam after death.
September 12, 2019 - The NFL announces that a total of $3 million has been made available in the "NFL Helmet Challenge," including $2 million in grant funding to support the development of a helmet prototype and a further $1 million prize for the winner.
August 25, 2020 - Two retired players, Kevin Henry and Najeh Davenport, file a lawsuit against the NFL for allegedly discriminating against Black players who submitted dementia-related claims in the "historic" concussion settlement. According to court documents, former NFL players being evaluated for neurocognitive impairment were assumed to have started with worse cognitive function if they were Black. So if a Black player and a White player received the exact same scores on a battery of thinking and memory tests, the Black player would appear to have suffered less impairment. And therefore, the lawsuit states, would be less likely to qualify for a payout.
June 2, 2021 - The NFL pledges to end "race-norming," a controversial practice that assumes Black players start with a lower level of cognitive brain function than other White and non-Black players, and to review previous test scores for bias in the settlement payout qualification process.