One of the best courtroom drama scenes in movie history broke the rules and did it in a way that did not take away from the film's authenticity. Remember this exchange?
Witness: You want answers?
Attorney: I think I'm entitled to.
Witness: You want answers?
Attorney: I want the truth!
Witness: You can't handle the truth!
Of course, this is the height of drama in the courtroom scene of A Few Good Men. This is the culmination of an epic battle between Tom Cruise as the defense attorney and Jack Nicholson as the witness.
This exchange is followed by a long recitation by the witness about the importance of the military to our ordered society even though we sometimes do not like the way they conduct their business.
This scene breaks the rules because trials are conducted in a question-and-answer format. The lawyer asks questions, and the witness answers. Here we have the opposite. The witness is asking questions and the lawyer is answering. Then the witness gives a long speech that is not in response to any question. (The objection there would be "nonresponsive" or "no question pending.")
However, it works for the story here because Tom Cruise's character is trying to push Jack Nicholson's character to admit that he gave the order that killed the victim and is therefore responsible for the death. It's an important reveal for the witness to explain why he does what he does even though most people would consider it "wrong."
More importantly, the movie can break these rules for the sake of drama without losing credibility because most of the movie is very authentic. There is an understanding of the way criminal cases and trials really operate that pervades the entire movie. That kind of authenticity throughout the story permits the knowledgeable viewer to forgive the occasional rule being broken. Especially when the result is such great drama!
The lesson is that breaking the rules doesn't take away from credibility when it is done conscientiously and with an understanding of the choices you are making.