Redskins rookie cornerback David Amerson is on the ground after the hit Sunday night that gave him his first concussion. (John McDonnell/The Washington Post)

He sat in his office at Navy Medical Center Portsmouth (Va.), a stack of records surrounding him, suspecting that bad news lurked in at least one of the folders.

Efland Amerson is a neuropsychologist, and he studies how concussions affect troops’ lives. Sometimes, as he did when he worked with athletes at the University of Virginia, he recommends life changes — a different job for a soldier, retirement from sports for an athlete. A few of those were on scholarship.

“Usually,” he said this week, “they know that it’s coming.”

On Tuesday morning, before examining the stack of cognitive test results, Amerson thought about what it would be like to deliver a similar recommendation to his son, Washington Redskins rookie cornerback David Amerson. Efland said he was in the stands Sunday night in Dallas when, during a kickoff return, Cowboys linebacker Cameron Lawrence crashed into the Washington rookie, knocking him out with a blind-side hit. Amerson later had a concussion diagnosed — his first such injury, the player said — and didn’t return to the game.

“One of those things,” David Amerson said a few days later. “Part of the football game.”

The Post Sports Live crew offers bold predictions for Sunday's Bears-Redskins game at FedEx Field. (Post Sports Live/The Washington Post)

But in the hours and days that followed, his father’s mind raced. Past retirement recommendations flashed back.

“That’s what I was thinking this morning: ‘What if that time comes?’ ” he said Tuesday.

The NFL has come under increasing fire the past few years over how teams handle players with head injuries even though rule changes have been made and resumed participation is closely monitored. But David Amerson still makes his living in a game that centers on quick comebacks from injuries, while his father makes his in a field that sees the worst of ignoring the long-term consequences of multiple concussions.

When Efland Amerson worked at Virginia, he saw the effects of repeated brain injuries. Athletes’ academic work and non-sports lives occasionally suffered.

Sometimes it took three concussions for test results to show longer-term injury, and for others it took seven or more, the elder Amerson said. But there he would sit, telling someone who had established at least part of his or her identity using sports that, in his opinion, it was time to leave it behind.

The alternative, as last week’s “League of Denial” PBS Frontline documentary repeatedly showed, could be long-term symptoms, such as memory loss or premature death. These are scenarios Efland is aware of — though he said he doesn’t like thinking about them befalling his son.

“My greatest fear,” he said. “From what I know from multiple concussions, it can be devastating.”

When the elder Amerson reached the visitors locker room Sunday night, he found David dazed and unaware of what had happened. Efland Amerson said his son didn’t remember Lawrence’s blind-side hit — which led to a $21,000 fine — or that he had been unconscious on the turf afterward. Still, David Amerson said he was “fine,” his father recalled, and said he wanted to return to the game, though since 2009, NFL rules have forbidden players from returning to games after displaying concussion symptoms.

“I knew the look that he had,” Efland said. “I see it all the time with the guys that I work with daily. I am a father. I was scared for him because he was just sitting there and he really didn’t know what happened.”

It is the kind of image that leads the elder Amerson to think about the future. He said he reminds his son often to protect his head, and this week he flooded his son’s phone with text messages and calls about being smart about his return to practice.

But the football culture is still one of toughness and quick recovery, no matter the injury. Although teams aggressively test players following concussions, part of the ramp-up protocol each injured player must pass before being cleared to return, the league is still trying to curb a decades-old culture of players hiding lingering symptoms.

This week, David Amerson insisted he was healthy, though earlier in the week his score on a follow-up concussion test “was low in one area,” he said. He retook the test, he said Thursday, and although the results were unknown, he seemed to be progressing toward playing Sunday against the Chicago Bears. He was a limited practice participant Wednesday and Thursday.

That hasn’t stopped the player’s father from sending more reminders to speak up if new symptoms reveal themselves during or after exertion or contact.

“I’ve had this talk with him when he was in college,” Efland said. “. . . After this injury, I just really need to reemphasize that with him again.”

David Amerson said Thursday that he and his father have a “mutual understanding” that he will be smart about protecting himself in exchange for Efland allowing his son the distance to make his own decisions. Efland said he understands that, regardless of his expertise, he must respect that his son is an adult with his own career to consider.

Still, the 21-year-old said, if his father felt strongly enough in the future to confront him about an early retirement, he would listen.

“It’d be something I wouldn’t be happy about,” David Amerson said. “But if it got to that point, you’d really seriously have to think about your future and just living, going on as a man, as a father, as a husband, whatever. . . . I would definitely listen to him.”

For his part, Efland said it’s too early to have those talks. If that day indeed comes, though, he said he would be comfortable in his role — even if it would mean asking his son to give up his livelihood, career dreams and, yes, part of his identity.

“It would not be tough for me to tell him that,” Efland said. “It would be very awkward position for him to make a decision. We’ve been telling him all along: ‘The NFL is temporary.’ ”

Nevertheless, he said, it was difficult to forget the look in his son’s eye and the confusion that followed Sunday night in Dallas.

“This is not a game,” Efland said. “And when you suffer these hits, the count starts.

“That’s your first one.”