There is a moment in the new documentary ‘‘Requiem for a Running Back’’ when director/narrator Rebecca Carpenter breaks down so hard over her late father’s tragic tale, weeping so uncontrollably with a proud daughter’s impotence, that little more needs to be said about the terrible, crippling toll of chronic traumatic encephalopathy.

As neurologist Julian Bailes says in the film, CTE doesn’t just affect the victim of the traumatic brain disease; it affects the victim’s entire family.

That is the true message of this stunningly gripping film, made by a woman who needed to know what was wrong with her father, 10-year NFL veteran Lew Carpenter, and with everything she had hoped would be so good about being in a die-hard football family.

Before the film had its Chicago debut Friday at the Gene Siskel Film Center, Carpenter spoke about the conflicting emotions she, her three sisters and her mother had about a man who played for the Lions, Browns and Packers before going on to coach for three decades.

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There were her dad’s mood swings and frightening actions coupled with his ceaseless pride in the dignity of the game. It left her confused about the macho sport, about its demand to suppress pain and injury and about the purported weakness it displayed if a man asked for help, particularly mental help.

As the old sign in the Eagles’ locker room warned: ‘‘BLAME NOBODY — EXPECT NOTHING.’’

Carpenter had heard about some of the groundbreaking concussion stories that were being pieced together by former Harvard football player Chris Nowinski and research pathologists at Boston University and elsewhere, but she didn’t want to hear it.

‘‘I was so mad at Chris Nowinski,’’ she said. ‘‘I thought he was a [wimp]. Football was a man’s game.’’

But something in her heart told her she was wrong. As former Packers tight end Paul Coffman says in the film, it actually takes more courage to admit one needs help than to hide one’s feelings and the intuitive knowledge that some problems are bigger than oneself.

And CTE is much bigger than anyone can deal with alone.

We have seen film archives about this topic grow, with Steve James’ ‘‘Head Games’’ and the Will Smith vehicle ‘‘Concussion’’ prime among the output. But for all the information about the connection between concussive and subconcussive head blows leading to the dementia and personality changes of CTE, powerful vested interests such as the NFL constantly downplay or obscure the dangers of the game.

Thus, it’s a battle of reality against disinformation, as public-health issues — such as smoking and global warming — so often become.

But when the pain of CTE trickles down and outward, crippling the lives of those who are clueless about how to deal with the destruction of their father/son/brother/grandfather, it’s wrong to pretend any of this is OK.

In the audience were a number of wives and family members of NFL players who died or are dying of CTE. They cried at the parts Carpenter cried at. They know, and they have been silent and confused for too long.

Candy Pyle, whose husband, former Bears center Mike, degenerated for years with CTE and died of it in 2015, agreed after the movie that Carpenter’s tale rings so very true.

‘‘Yes,’’ she said. ‘‘All of it.’’

Lew Carpenter’s brain was dissected several years after his death at age 78 in 2010 and was found to be riddled with the tangled tau protein indicative of severe CTE. Dr. Ann McKee, who did the dissection in Boston, told Rebecca Carpenter in the film that it was amazing her father functioned so well for so long before succumbing.

Carpenter, a skilled storyteller with a fine-arts degree in filmmaking, spent 3½ years and virtually all her savings making this documentary. It has helped her become, she told me, ‘‘100 percent complete.’’ Moreover, she said, it took many others with similar experiences to help her finance and produce the film.

‘‘I was living with a big question mark,’’ she said. ‘‘Why couldn’t I connect with my dad in a way that felt normal? Now I know.’’

She smiled at the dark irony of her dad’s legacy.

‘‘I’m a football coach’s daughter,’’ she said. ‘‘You leave everything on the field. And I did.’’

Follow me on Twitter @ricktelander.

Email: rtelander@suntimes.com