Author Joseph Wambaugh disowned, disavowed, and de-credited himself from this adaptation of his book "The Choirboys". Wambaugh was so incensed with this adaptation of his book, considering it to be such a poor adaption, that he sued the production, and was successful in having his name removed from the film's credits.
After the way his novel was adapted for this film, Joseph Wambaugh decided to take more control of his literary works, having a much larger influence on the production of The Black Marble (1980) and The Onion Field (1979).
Walter McGinn played the role of Sergeant Nick Yanov, but was killed in an auto accident on March 31, 1977, after the third day of filming. He was replaced by Charles Haid.
The movie's ending is completely different to the one in the novel.
The title was derived from the activities of the story's police officers, which they call "choir practices". These are drunken parties that the cops throw in order to let off steam from the stress and pressure of their jobs.