Many of my favorite documentaries over the years have been works of cultural historiography — films that literally “write the book” on some corner of pop culture that’s outside of my experience or general interest.

My first serious education in hip hop was “Rhyme & Reason.” “Paris is Burning” introduced us all to drag queen subculture’s embrace and impersonation of high fashion. “The King of Kong” packaged video gaming’s prehistory into a tale of hated champion vs. upstart challenger, and “Rize” set the table for how dance culture got from hip hop to krumping and clowning, to twerking.

“When the Beat Drops” peels back the layers of recent dance history, the line dancing “dance battles” first mainstreamed in “Stomp the Yard” and “Step Up” and “You Got Served,” and traces it to the ascendant Capital of African America — Atlanta — and the black gay subculture that created it.

Jamal Sims’ film breaks into chapters focusing on this or that figure in Atlanta line-dancing’s past and present.

It all began, the various practitioners of the back-arching, leg-kicking “buck” dancing say, with the majorette/dance squads of “HBCUs” — Historically Black Colleges and Universities — with Atlanta’s Clark, Spellman, Morehouse, Morris Brown and Spelman at their epicenter.

Football and basketball games brought in not just the athletes of Jackson State, from Jackson, Mississippi. It was the dance squad, the Prancing J-Settes that won the attention, admiration and imitation of young Anthony Davis and his friends.

A plus-size kid who had grown up with little interest in “doing what boys should do,” who knew he was different when he realized Lynda Carter’s “Wonder Woman” was his role model, Davis would watch the “graceful…sassy and sexy” J-Settes, and he and friends would try out what they saw that night, after the game, in Atlanta’s African American dance clubs like Club Traxx.

“Bucking…like a stallion,” was all the rage, and the dance floor and even the parking lot would be the scene of dance battles as young men would throw down, match each other’s moves and try to better them.

Davis founded his own dance team, Phi Phi, which has ruled the roost in Atlanta, hosting and sponsoring competitions, demonstrations and the like, gay teams putting themselves out there in increasingly feminine attire in a conservative, church-based bastion of African American conservatism. “The city too busy to hate” would slowly come to accept its black gay subculture.

Made-up and dressed in matching halter-tops, leggings and boy shorts, groups like Team Mystique and Banji and 3D would dance-off in assorted styles of music — House and Hip Hop.

Official competitions, which Davis and Phi Phi often organize (as they moved away from competing) would feature a category called “Stands” — dance moves a college dance squad like the J-Settes could perform in the limited space, on steps, aisles or in between seats, in the stands of a football stadium or basketball arena.

“Dance in YOUR SPACE,” Anthony, aka “Big Tony,” bellows to his team as they practice choreography, barking out the count as they rehearse their steps.

Dancers talk about the grounding they need in modern dance, jazz dance and ballet and use the nomenclature of those disciplines, even if they never formally studied them.

As “bucking” came to be known as “J-Setting,” named for Jackson State’s dancers and their role in inventing and popularizing it, a new generation of dancers like Lavor and Napoleon (Team 3D) got involved and all of this moved even more out into the open.

As “Napoleon” (Lynel Goodwin) may declare, “When the beat drops, my mission is to take over the world.” When he’s not in dance mode, he’s a school band teacher and non-profit director (Band Room Nation), popularizing marching/dancing bands at high schools across America.

Those profiled talk about getting mugged, harassed and discriminated against, and debate how “out there” they should be when, for instance, they participate in a small town Christmas parade.

Sims has gone for an action-oriented (lots of dancing) and yet intimate, in-their-own-words story which hamstrings his film somewhat. That myopic approach means there’s no outside voice connecting this trend or fad to the larger dance world. It’s just gay black dancers in Atlanta chronicling dance inside their bubble, with no Voice of Cultural Authority saying, “It spread from here to the horizons” or “This will be as forgotten as krumping in a few year’s time.”

Still, “When the Beat Drops” makes for a fascinating dissection of “how these things get their start,” even as the jury’s still out on their larger impact.

fascinating  I did not know that

MPAA Rating: unrated, profanity, sexuality

Cast: Anthony Davis, Lynell Goodwin, Johnny Waters III

Credits:Directed by Jamal Sims. A World of Wonder/LOGO release.

Running time: 1:27