What is the point of introducing and disclosing evidence planned to use during trial before trial? Doesn't that let the other party know what evidence a party is going to use and allows the other party time and opportunity to counter them during trial?

@HelloDarkWorld Yes. That’s the point. Trials are decided on the evidence known to all not because one side knows something the other doesn’t. Drop-mike a-ha moments are vanishingly rare in a courtroom.

More to the point: The trope where somebody bursts into the courtroom with evidence that ends the trial and frees the wrongfully-accused defendant is a TV-and-movies thing, and not a real-life thing.

@EvilSnack Pretty much, but I have come close to that in at least one case, and there is more latitude for late disclosed evidence from criminal defendants.

I appreciate that questions are often modified over the life of a Q&A, but I don't think we want to start quoting the Q in the A. Excellent answer otherwise, +1

@EvilSnack: Surprises don't happen very often, but they can happen.

@DaleM If trials are decided on the evidence known to all not because one side knows something the other doesn’t, then how does one party able to argue to persuade the judge and jury to believe his or her side of the story?

@HelloDarkWorld By showing that there is a preponderance of evidence or whether the evidence proves one's claim bexond reasonable doubt. In addition there are often further questions to resolve like how much of the damage can be attributed to the defendant, whether a damage estimate admitted to evidence is relevant and reliable etc.

What if the other party did not request for production of certain documents during discovery that will be advantageous to them during trial but I take advantage of and use these documents to prove my case during trial, is that allowed?

While evidence and the list of witnesses has to be disclosed, there can still be surprises in the testimony, right? Or does the other side generally get to depose witnesses before the trial, so they can try not to be caught by surprise?

@Barmar Yes, though the typical adage is that no (good) attorney asks questions they don't already know the answers to, or puts up a witness who would provide unexpected answers. But sometimes stuff happens. Heck, Trump's NY fraud trial had just such an issue, where Weissman was called out for apparent perjury in near real time by a news organization, resulting in an abrupt end to his testimony (and allegedly there are now talks of a perjury plea agreement, which may be delaying the final judgment in said case).

@zibadawatimmy I meant a surprise to the other side, not to themselves.

@Barmar For that see Kevin's comment that links to a "gotcha" moment against Alex Jones. It's very rare. We're basically seeing it several times right now because there are multiple pugnacious personalities who are under the spotlight and have been obstructing and delaying discovery against them, making it significantly more likely that whatever information does get out undercuts the claims they've been making in court.

@zibadawatimmy That's surprising the witness. I mean a defense witness giving testimony that surprises the prosecution, or vice versa.

@Barmar For that see Weissman. That was a bizarre situation: he had a plea deal with the prosecution, but was siding with and taking legal counsel from the defense; his severance package even required non-cooperation with authorities "except when required by law". And I'm not sure either side expected him to perjure himself on the matter at hand, in part because I don't think either side knew of the evidence that this news organization had that would flatly contradict the claims he was making on the stand, under oath.

@zibadawatimmy How is a witness perjuring themselves a "gotcha"? I'm just asking about a situation where someone gives normal testimony that the opposition could not have anticipated and prepared to rebut. Do they get to interview the witness before the trial as preparation?

@Barmar "Do they get to interview the witness before the trial as preparation?" Yes. Usually through depositions. But not all witnesses (especially minor ones) are deposed. Someone can also be impeached through voluntary witness interviews pre-trial that are deviated from at trial (I've done that).

@ohwilleke common law jurisdictions other than the USA do not require US-style depositions (though the parties in a civil trial can agree to them and in arbitrations evidence-in-chief is almost always provided in writing before the hearing). Discovery is limited to documents including expert reports and a list of witnesses. That does allow for slightly more room for surprise in evidence unsupported by documents … but if you’re building a case on that …