I love skateboarding, both the physical feeling and aspects of the culture, and skate videos are where the physics and culture collide. These days, the tradition of the sponsored group skate video is under siege by unaffiliated prodigies on Instagram. (The skating arms race has accelerated to the point where little kids rip as hard as the teenage pros of the eighties.)

To me, this seems inevitable but a little sad, because seminal videos form a record of skating’s technical and cultural evolution: the prelapsarian innocence (before Bam Margera and the X Games) of 1987 Bones Brigade classic The Search for Animal Chin; Margera’s nihilistic, violent CKY series a decade later (which gave the world Jackassyou’re welcome?); and the skate mag Transworld‘s cool, arty rebuttal, In Bloom.

While some skate videos have stories and expensive production, others are the result of children being turned loose on the streets with cameras and boards to see what happens. These are a very particular type of documentary, equal parts visual poem, highlight reel, and advertisement. Real life gets in through the convention of editing bits of spontaneous horseplay between the lines, and tricks are verifiable events in the world. But they were staged over and over to achieve the desired result, and we usually don’t see the fifty painful tumbles off the rail.

If skate videos are all about enshrining glory, skate documentaries tend to be much bleaker affairs, illuminating the dark backdrop of the joyous oblivion all pushers seek. After all, as much as skating is toward pleasure, it is also away from pain. Most skate docs are about great skaters: my favorite is Rising Son: The Legend of Skateboarder Christian Hosoi, which chronicles the rise and fall of the skate artist whose soulful bravado played counterpoint to Tony Hawk’s robotic precision back in the day.

Minding the Gap, showing at Full Frame on Saturday, is something else again: it’s a doc about a group of average skaters. With the glory stripped away, only the question remains: Why do they abuse their bodies by leaping around sharp bits of concrete and metal on finicky wheeled boards? The answer is that it shoots them out of a grim gantlet of child abuse, racism, parental neglect, and postindustrial decay. It becomes easy to see why improvised families take shape in such an inhospitable void.

For ten years, the young director Bing Liu filmed his friends in Rockford, Illinois, a truly rusty Rust Belt town that they traverse by wooden toy, their simple ollies and shove-its developing into solid kickflips and airs over the years. Three main characters soon emerge from the scrum. Zach, the film’s id, is handsome, charismatic, hedonistic, and, we soon gather, inexplicably tortured. But at first, he’s all party.

“Are you going to put me smokin’ weed in the thing?” he asks Liu, breathing out fumes. “I’ve given you free range. I have no stipulation.” Then he shotguns a PBR. Zach fights terribly with his baby’s mother but is surprisingly tender with the baby. His arc, the film’s most troubling, is about his relationship with the mother (she gets her own arc, too) and his fitful attempts to grow up, frequently backsliding and replicating the cycle of abuse he has in common with all his friends.

Keire, the film’s heart and soul, is almost the only African-American kid at the skate park. Sweet and self-conscious, radiating embarrassedly suppressed delight, he finds a kinship among skaters that he doesn’t find at home, where he stands out with his tie-dyed T-shirt and electric guitar. But we also see his alienation when his friends repeat or laugh at pop-culture racial slurs, and he sometimes destroys decks in anger. When asked how he was disciplined as a child, he explains mildly, “Well, they call it child abuse now.” His arc is about getting over his father’s death and breaking free from Rockford.

Finally, there’s Bing, who, as cameraman and director, is essentially the film’s god or conscience, which are maybe different ways of saying the same thing. Quietly and thoughtfully, he steers the film toward confronting and healing everyone’s wounds, from his own mother’s choices to Zach’s alcoholism and abusiveness. Bing’s moment with Keire near the end (you’ll know it when you see it) is now seared on my heart forever. He doesn’t redeem Zach but doesn’t quite damn him, either, though Zach seems intent on damning himself, as is borne out in his cathartic final speech.

Who is Zach? This is the enigma at the center of the film. “Some people do take their negative experiences and turn them into powerful positive things,” he says. “I just don’t think I’m that type of person.”

But what Liu renders crystal-clear in Minding the Gap is that all his friendsand indeed, many skaters around the world and throughout timeare trying to make up for families and societies that let them down, trying to build adulthood atop childhoods they feel they didn’t have. It’s a hard lesson, but one rendered tolerable, for us and for the film’s subjects, by the frame of skating’s lyric poetry in space, its stubborn grace against all odds.