“I don’t think we can conclude what exactly caused this,” said Dr. Julian Bailes, a neurosurgeon at West Virginia University and a former Steelers physician who has seen Strzelczyk’s pathology report. “Although if you go through the list of potential causes, certainly trauma to me is No. 1. Is that football trauma? Is that NFL trauma? Is that high school trauma? Is that falling off a bike as a kid? I don’t know.”

Bailes is also the medical director at the University of North Carolina’s Center for the Study of Retired Athletes, which found in a recent study of more than 2,500 retired NFL players that those who had at least three concussions during their careers had triple the risk of clinical depression as those who had none. And those who recalled having one or two concussions were 1½ times more likely to be diagnosed with depression.

The study involved only those concussions suffered in the NFL, even though players may have also had some during high school and college. Many were active before the league began its concussion management program in the mid-1990s and before studies sponsored by the NFL and NCAA prompted new helmet designs.

The NFL questioned the findings but is conducting its own study on retired players.

Concussions can be difficult to diagnose, and players who were conditioned when they were children to play hurt are reluctant to reveal injuries.

“Who wants to come out of the game?” wondered Vincent, who has been diagnosed with six or seven concussions in 15 seasons. “No player wants to sit on the sidelines.”

And if a coach asks if a player is OK?

“When you’re asking a player on the sideline if he wants to go back in the game, the answer is going to be yes,” said Mark Bruener, a member of the NFLPA’s board who has been diagnosed with four concussions in 12 seasons.

Former New England linebacker Ted Johnson told The New York Times in February he wasn’t given a choice. And now, he’s showing signs of early Alzheimer’s disease.

Johnson told The Times his mental problems began in 2002 when he had two concussions in four days — during an exhibition game and then after coach Bill Belichick pushed him to join full-contact practice against the advice of the team’s top trainer.

The whistle-blower system might prevent problems. More education should help, too.

“I think players will do a better job policing,” Vincent said. “You’re in the huddle, you see your colleague’s dinged, just tell the official. Now, because of the attention that it’s getting, I think the officials will be more aware, and the players in the huddle will be more aware.”

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