Parents have been worrying about their sons playing football for more than a century now, but the past decade has provided more to worry about than ever.

Broken necks and mangled legs were scary enough; scrambled brains are worse in a way, given the initially hidden nature of the threat.

Into this fraught environment comes the film “Concussion,” its topic self-explanatory.

Football executives and fans have been awaiting its Dec. 25 delivery as if it were a lump of coal, wondering just how badly it would reflect on the modern national pastime.

Let’s put it this way: You know those reports from hacked Sony emails suggesting the script might be scrubbed to go easier on the NFL?

If there was a version that was going to be even tougher on the continent’s most powerful sports entity, well . . . yikes.

“Concussion” is a blunt indictment of how the NFL handled brain injuries for decades, up to and including the 2000s.

It centers on the story of Dr. Bennet Omalu (Will Smith), a Nigerian forensic pathologist who in 2002 performed an autopsy on former Steelers center Mike Webster that led to a diagnosis — and naming — of chronic traumatic encephalopathy, or C.T.E.

Many years of legal, financial, research and public relations wrangling have ensued, along with the premature deaths of several more prominent former players, most notably and recently Junior Seau.

But you knew all that, and therein is the challenge of commercial viability for “Concussion” as a scripted, based-on-fact movie rather than a documentary. (It is based on a 2009 article in GQ magazine.)

Will it tell those who have followed this story with interest over the past decade things they did not know? Not really.

More importantly, will it reach those who have either ignored or eventually tuned out the story amid the drone of bad news? Probably not.

The film is earnest and well-acted by Smith, complete with a believable African accent, but is about as subtle as — OK, I’ll say it — a blow to the head.

Most moviegoers looking for Christmas-week entertainment are apt to look for something a tad less depressing than making them feel guilty about one of their favorite indulgences.

This is a tough sell, like telling people that buying Adele albums could be hazardous to her long-term health.

“Concussion” is a mashup of important medical research, one dogged immigrant’s battle against authority and accepted wisdom, plus a love story thrown in to (sort of) lighten things up.

Not that there’s anything wrong with all that. But given how recent these events are and how well we know the movie’s bad guys — in this case, mostly the NFL — the lack of nuance is jarring.

Smith seems to be under siege by everyone from the Feds to mysterious people tailing his wife’s car for no directly obvious reason. It’s all just part of the sinister forces seemingly out to get him.

Luke Wilson appears as NFL commissioner Roger Goodell with his hair too dark but his disconnected tone about right. Others associated with the league come out of it much worse, including former Jets doctor Elliott Pellman.

It took far, far too long for the NFL to come to terms with the threat posed by brain trauma to its players, not to mention to the future of American football in general.

But thanks to pressure from people such as Omalu, progress is being made to the extent it is possible given the nature of the sport.

An NFL spokesman offered the following when I requested a comment about the film:

“We welcome any conversation about player health and safety. Broader and deeper awareness of these issues will positively impact all athletes. The NFL has made numerous changes to the game to enhance the health and safety of players at all levels of football.

“These include nearly 40 rule changes in the last decade, strict concussion protocols, and better training and sideline medical care. We are seeing measurable results, including a 34-percent decrease in concussions in NFL games since the 2012 season.

“Additionally, we are funding independent scientific and medical research and the development of better protective equipment to advance further progress. The game continues to change, and the safety of our players remains our highest priority.”