It was an ordinary play in a big game, and maybe the combination of those two factors caused Malcolm Jenkins to disregard the telltale fogginess that began to settle over his consciousness.

Cowboys running back Darren McFadden had broken free of one tackler in the second quarter of the Eagles' 33-27 victory Sunday in Dallas and was moving forward. Jenkins - the Eagles' starting strong safety, as intelligent and respected as any player in their locker room - moved forward, too, to confront him. Jenkins led with his right shoulder when he collided with McFadden, and still his head struck McFadden's chest with enough force that, once Jenkins got up from the ground after making the tackle, he felt something he had never felt before. The game's action seemed faster, he said, and he didn't know where to train his eyes to see what was happening, and he realized he'd suffered his first concussion.

He did not tell the Eagles' coaches. He did not tell the Eagles' team doctors or trainers. He knew he should tell them, but telling them meant he'd have to go through the NFL's concussion protocol. He'd have to come out of the game. Jenkins didn't want to do that. The risks of chronic traumatic encephalopathy, of dementia, of all the afflictions that might torment any athlete who has suffered one or more head injuries - none of them were as important to Jenkins as playing in that game was.

This is the loophole in every effort by every major sports organization to reduce or better treat head injuries: the athlete's own free will. Unless the incident that causes the head injury is so obvious as to be impossible to ignore - and sometimes even when the incident is so obvious - the athlete can always try to hide what's happened from the people who need to know. The athlete wants to help his team win. He doesn't want to lose his spot in the lineup, to be Wally Pipped by his backup. He wants his teammates to know he's tough. He wants to keep his career alive. So he will say he's fine, even now, even when concussions have become the hot-button health topic in sports, even when Will Smith stars in a film called Concussion that will be released in December and that promises to both dramatize and criticize the NFL's negligence with respect to head injuries.

That's the thing: Jenkins is not the exception, not in the NFL, not in any sport. Go back to last year's NHL playoffs, when Flyers goaltender Steve Mason nearly singlehandedly stole a first-round series from the New York Rangers - yet was still experiencing concussion symptoms when the series began.

"They had to hold me back," Mason said after the series ended. "I told them I could keep playing. 'I could play with this.' And they were like, 'No, you've got to sit out, blah, blah, blah.' "

Go back to July 2010, when Jason Bay, then an outfielder for the New York Mets, crashed face-first into the left-field wall at Dodger Stadium after catching a fly ball, his head recoiling as if he'd been in a car crash. He played the next two games, then sat out the rest of the season, and still in September he stood at his locker in the Mets' clubhouse at Citi Field and said: "There's a part of me that says, 'If you've gone through all the stuff and you're ready to play, why not?' . . . If there are two games left [in the season], OK, maybe not. But if there's more than that, I could and should play."

Better yet, go back to a phone call to former Flyers captain Keith Primeau, one of many interviews he has done since September 2006, when he retired because of post-concussion symptoms. Primeau has been susceptible to fatigue, light sensitivity, and headaches since his career ended. He has agreed to donate his brain posthumously to Boston University's Center for the Study of Traumatic Encephalopathy, so doctors can study it. He played through concussions just like Jenkins played through this one, and he kept his mouth shut for the same reasons that Jenkins said nothing to an Eagles coach or trainer Sunday night.

"That's the biggest dilemma," Primeau once said. "A trainer goes to a player and says, 'How do you feel?' If you're competitive by nature, you don't give the honest truth. Try to tell a competitive, professional athlete - whether it's hockey or baseball or football or whatever - to tell the honest truth. You're probably not going to get it. And that's what players have to come to understand: There is a consequence to that decision."

Malcolm Jenkins understood, in the moment, the consequence of his decision. He went back on the field anyway. He said Thursday that he feels fine now, that he was stupid, that he was lucky. He ought to keep saying that, tomorrow and the next day and the next day. One of the smartest men in the Eagles' locker room didn't listen to himself, but maybe another athlete will.

msielski@phillynews.com

@MikeSielski