The poster for the documentary “On the Line: The Richard Williams Story” is cleverly acerbic. Against a white background stands one of the more derided — and more recently celebrated, via last year’s sports biopic, “King Richard” — figures in professional sports: Venus and Serena Williams’ father, Richard. He’s got a tennis racket in his hand and is clad in throwback tennis whites. It was not typically what he wore as he and wife Oracene (Price) trained their daughters on the public courts of Compton, Los Angeles. But the look was de rigueur for the white tennis establishment that Venus and Serena took on and then transformed.

In “On the Line,” Williams has his say. Unsurprisingly, he’s frank, occasionally funny, but also vulnerable, not least because he’s growing frail, having suffered from health issues. As directed by Stuart McClave, the documentary isn’t exactly a vanity project, but...