One difference between the stage version and the movie version is the name. The play is called A Soldier’s Play. The movie is called A Soldier's Story. This difference might seem cosmetic or superficial, yet the switch from “Play” to “Story” seems to prepare the viewer for the differences. It tells the viewer that they’re watching a relatively more popular, more mainstream genre—i.e., a movie. Alas, the viewer should get ready for some of the common devices that tend to be found in mainstream movies, including slow motion.
You might have noticed multiple slow-motion moments in A Soldier’s Story. When the Sergeant is first shot at the beginning of the film, the director, Norman Jewison, employs slow motion. When CJ hits a home run, Jewison again uses slow motion. In the play, of course, there is no slow motion.
Another difference is the end. In the play, the conclusion comprises Davenport telling the audience what happened. Peterson was captured one week later in Alabama. Davenport never confronts Peterson directly like he does in the movie. In the film, as you might remember, Davenport not only faces Peterson, but he lectures him. He tells Peterson he doesn’t get to “judge” who does and does not qualify as Black.
As for similarities, there are quite few. Perhaps that’s because Charles Fuller, the playwright, wrote the film adaptation as well.
The film keeps the nonlinear narrative. As with the play, it jumps back and forth between the present and the past.
It also keeps the highly radicalized language. This might be notable because recent mainstream films—like Green Book—have been criticized for portraying race in a rather censored, whitewashed way.
Lastly, the film preserves the musical aspect. Although, in the play, the song “Don’t Sit Under the Apple Tree” is used multiple times. In the movie, you might only hear the song once. Although, as you might recall, you will hear several other songs. The opening song, for instance, is sung by the famous Patti LaBelle.