While most of the early retirees didn't specifically cite injury fears, Borland said that concerns about repetitive head trauma drove his decision. Concussions have become an ongoing point of contention in the league as some former players have been diagnosed with chronic traumatic encephalopathy, a brain disease.
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"By any measure, football has never been safer and we continue to make progress with rule changes, safer tackling techniques at all levels of football, and better equipment, protocols and medical care for players. Concussions in NFL games were down 25 percent last year, continuing a three-year downward trend," the NFL said in a statement responding to Borland's retirement.
Educating players about head injuries and handling them correctly once they happen is crucial, Brewer said. As more information about the long-term effects of head injuries becomes available, more players will step away from the NFL early, he said.
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Concussions have become more of a concern because the league documents them much better than in the past.
"I think now we have more concussions because we are actually tracking them," he said.
Brewer noted that he sees more "concern" about head injuries than when he played in the early-2000s. During his career, he would see "laughter and high-fives" after a player got "knocked out" by a big hit.