Yes, we already know there’s a connection between a career in football and the likely occurrence of multiple concussions and possible long-term brain damage.

The PBS “Frontline” documentary “League of Denial,” the Will Smith drama “Concussion” and books such as “Counting the Days While My Mind Slips Away” preceded Rebecca Carpenter’s “Requiem for a Running Back” — but Carpenter’s ★★★★ film might be the most searing, most powerful, most personal and most unforgettable take on this most American of tragedies.

Lewis Carpenter was an early NFL star. He played on three championship teams in the 1950s and 1960s, and then spent 31 years as a coach in the league. Carpenter was a handsome, charismatic, imposing, mercurial figure — larger than life to daughter Rebecca.

Mr. Carpenter was diagnosed postmortem with Chronic Traumatic Encephalopathy (CTE), which led to Rebecca embarking on a multi-year journey to re-examine her upbringing, to talk to NFL legends such as Mike Ditka about CTE, and to conduct interviews with former teammates of her father as well as former players he coached.

The end result is a brilliant and brave and beautifully honest film.

★★★★

Hydro Studios presents a documentary directed by Rebecca Carpenter. No MPAA rating. Running time: 89 minutes. Opens Friday at the Gene Siskel Film Center. Carpenter and producer Sara Dee will introduce the 6 p.m. Friday screening, and the 7:30 p.m. Saturday screening will be followed by a panel including Carpenter, Dee, neurosurgeon Dr. Julian Bailes, journalist David Maraniss, and former San Francisco 49er Chris Borland.