The Choirboys is basically about a group of LAPD policemen who let off the stress of their regular jobs by engaging in some rather "interesting" after hours activity.
It also included early appearances by stars like Louis Gossett Jr. (five years before Officer & a Gentleman) and Charles Durning.
Both Gossett and Durning were well-established character players by the time of THE CHOIRBOYS and were, arguably, the biggest names in the cast, although Perry King was pretty famous at the time for one of those miniseries he did. Gossett had begun working in film and television regularly starting in 1961, although he has one earlier credit on IMDB, while Durning had started working regularly in 1962, with one much earlier credit listed on IMDB.
Ten years earlier he would never have made either The Choirboys or The Legend Of Lylah Clare.
In fact, he DID make THE LEGEND OF LYLAH CLARE ten years earlier--or close to it. LYLAH CLARE came out nine years before THE CHOIRBOYS.
I saw THE CHOIRBOYS at a preview screening in December 1977 and the film school buddy who accompanied me came out of it saying it was one of the five or six worst films he'd ever seen. I happened to like it, because it deliberately punctured all that "Blue Knight" romanticism about cops that Joseph Wambaugh spent his literary career promoting and which had infused such film adaptations as THE NEW CENTURIONS and the long-running TV series, "Police Story," which was still airing when this film came out. Aldrich was indeed undercutting Wambaugh with this film, to the point that Wambaugh, whose book it was based on, sued to take his name off the film (he lost the suit).
It was also something of a response to the Dirty Harry series of films and their celebration of an infallible cop hero who shoots first and asks questions later and violates civil liberties in a case of the ends justifying the means. There's even a scene where one of the cops responds to a potential roof jumper in much the same way that Harry did in DIRTY HARRY, but with very different and more tragic results.
It is a bizarre film, though. If it was aiming for gritty realism, it sure didn't succeed, with all of its garish studio lighting and obvious studio sets. Certain things in it seemed awfully sensationalized, e.g. the s&m subplot. But it's got an incredible cast. Aside from Gossett, Durning and King, it had James Woods, Randy Quaid, Burt Young, Don Stroud, Tim McIntire, Robert Webber, Jim Davis, Vic Tayback, Jeannie Bell, Phyllis Davis, Barbara Rhoades, Bob Minor, Maria O'Brien (daughter of Edmond) and the unforgettable Rainbeaux Smith (billed as Cheryl Smith) as a pregnant streetwalker.