Journal of the American Medical Association study finds abnormalities in almost 50% of boxers who remained in the sport for several years.

American Football Coaches Association declares that concussed football players should leave the game for personal attention.

New York State Legislature creates the Medical Advisory Board for the New York Athletic Commission to curb health risks for boxers. Three-year study devised six measures to avoid brain damage and “punch drunk” syndrome, among other injuries.

Journal of the American Medical Association publishes a study on the encephalopathic changes in boxers.

New England Journal of Medicine recommends that football players leave the sport after suffering three concussions.

Two doctors examine the heightened incidence of chronic encephalopathy in boxers and characterize it as a “Parkinsonian” pattern of progressive decline.

Study published in Lancet shows that some boxers sustain chronic encephalopathy as a result of repeated head impacts.

The Journal of Medicine and Science in Sports recommends that any concussive event with transitory loss of consciousness requires removal from play and monitoring.

Second Impact Syndrome is identified (although not so-named in 1984), whereby a subsequent impact to a concussed brain leads to severe swelling. Forty football players have died of this syndrome.

Drs. Gronwall & Wrightson perform study on non-athletes and find that those who suffered two concussions took longer to recover than those who only had one.

UVA and other institutions study college football players who had suffered MTBIs, determining that they experienced long-term pathological damage. UVA also concludes that a player who had suffered one concussion was more likely to suffer another one, especially if the first was treated poorly.

Dr. Cantu of the American College of Sports Medicine publishes the Concussion Grading Guidelines (which are updated in 2001).

The NCAA implements across-the-board head injury safety guidelines for all sports, including  criteria to protect players even remotely suspected of having sustained concussions.

WBC (Boxing) and NCAA football create strict return-to-play criteria for football players suspected of suffering head injuries.

NFL creates the Mild Traumatic Brain Injury (MTBI) Committee to research and study the effects of MTBI on NFL players. NFL commissioner Paul Tagliabue appoints Dr. Elliot Pellman, a paid team trainer with no specialized training relating to concussions, to lead the committee. Roger Goodell was VP and COO at the time.

UNC National Center for Catastrophic Sport Injury Research conducts a study of 18,000 collegiate and high school football players showing that a player suffering one concussion was three times more likely to suffer another one in the same season.

Poll of 1,094 former NFL players shows 60% had sustained a concussion, while 26% had sustained three or more. Fifteen percent had suffered five or more.

Dr. Omalu examined the brain tissue of deceased NFL players and determined that the players suffered from Chronic Traumatic Encephalopathy (CTE). His work was published in Neurosurgery.

The MTBI Committee asks Neurosurgery to retract Dr. Omalu’s work.

NCAA study of 2,905 football players showed that those who have suffered a concussion are more susceptible for up to seven to ten days post-injury.

UNC Center for the Study of Retired Athletes study shows a link between multiple concussions and depression among former players with a history of concussions.

MTBI Committee releases first findings on active players, stating that concussions had no long-term negative health consequences.

Dr. Guskiewicz analyzes data from 2,500 retired NFL players and finds that 263 suffered from depression. His study found that having three or four concussions meant twice the risk of depression as never-concussed players. Five or more concussions led to nearly three times the risk.

New York Jets receiver Wayne Chrebet is knocked unconscious during a game. After Chrebet regains consciousness Dr. Pellman, head of the MTBI Committee, reportedly tells Chrebet “this is very important for your career,” and sends him back into the game. Chrebet would later be diagnosed with post-concussion syndrome.

Neurological convention in Prague coins the phrase “when in doubt, sit them out.”

MTBI Committee publishes a report stating that there was no risk of repeated concussions in players with previous concussions and no seven to ten day window of increased susceptibility.

An independent expert writes that the NFL study “contradicts literature published over the past twenty years,” and says that it sends dangerous messages to players.

MTBI Committee releases a paper in December Neurosurgery on testing 655 players and concluding that NFL players did not show a decline in brain function after suffering concussions, as well as no ill effects for those who experienced three or more.

UNC Center for the Study of Retired Athletes follow-up study shows a connection between concussions, brain impairment, and Alzheimer’s disease in retired NFL players.

MTBI Committee concludes that “Return to play [from concussions] does not involve a significant risk of a second injury either in the same game or during the season.”

Dr. Guskiewicz performs follow up study of 2,550 former players and determines that players with three or more concussions were five times more likely to have mild cognitive impairment than players without a history of concussions.

MTBI Committee rejects all findings put forth by Drs. Guskiewicz, Cantu, Omalu, and Bailes at a concussion summit for all team doctors and trainers.  The committee denies that CTE had ever been scientifically documented in football players.

UNC Center for the Study of Retired Athletes publishes survey-based reports detailing a correlation between dementia, depression, and other cognitive impairment in NFL players and how many concussions they suffered.

The NFL publishes a pamphlet to players stating that “Current research with professional athletes has not shown that having more than one or two concussions leads to permanent problems if each injury is managed properly.” Meanwhile, the MTBI committee denies that CTE has ever been documented in football players.

Dr. Casson of the MTBI committee states on television that there was no link between concussions and depression, dementia, Alzheimer’s disease, or “anything like [that] whatsoever.”

Boston University study by Dr. Ann McKee finds CTE in two more deceased NFL players. She stated that the simplest way to reduce CTE in contact sports was to decrease the amount of concussions.

An NFL-commissioned study of 1,000 former players, conducted by experts at the University of Michigan found a heightened occurrence of Alzheimer’s and memory related diseases, including a rate 19 times the normal rate for men ages 30-49.

The NFL distances themselves from the study they commissioned, calling it incomplete and inconclusive.

At a U.S. House of Representatives hearing, NFL Commissioner Roger Goodell acknowledges the NFL’s unique position of influence over the entire football community: “In addition to our millions of fans, more than three million youngsters aged six to fourteen play tackle football each year; more than one million high school players also do so and nearly seventy five thousand collegiate players as well. We must act in their best interests even if these young men never play professional football.”

Dr. Omalu tells members of Congress at a forum in Texas that “We have known about concussions and the effects of concussions in football for over a century.”

Dr. Casson of the MTBI committee tells members of Congress at a hearing in Detroit  that “[t]here is not enough valid, reliable or objective scientific evidence at present to determine whether or not repeat head impacts in professional football result in long term brain damage.”

Scientists discover a link between multiple concussions and ALS.

NFL changes the MTBI Committee to the “Head, Neck, and Spine Medical Committee,” and replaces its chairmen.

New England Journal of Medicine article describes the consequences of mild traumatic brain injury (TBI), which include CTE, early-onset Alzheimer’s.

The NFL’s new committee admits the work done by the MTBI committee was “infected.” Co-chairman Dr. Batjer says that the MTBI committee had an “inherent conflict of interest” that “was not acceptable by any modern standards.”

Dr. Berger of the NFL’s new committee says that there was “no science” in the MTBI Committee’s long-term study.