Attorneysand witnesses
A side is built out of two kinds of work. Attorneys argue the case; witnesses are the case. Both sides work from the same packet of affidavits and exhibits, so what separates them is how each role is prepared and cast.

Roles on a side
Attorney
Gives the opening and the closing, takes the side's own witnesses through direct examination, and goes at the other side's witnesses on cross.
Witness
Takes the stand in character, tells the story from the affidavit on direct, and has to hold that story together while the other side pulls at it.
Attorney and Witness
Prepared both ways, and cast into whichever one the round turns out to need.
Timekeeper
Keeps each side's clock and signals the attorney at the bench when the time is nearly gone.
The affidavit
Every witness in a mock trial case comes with a sworn affidavit, and that affidavit is the whole of what the witness knows. On the stand the witness answers as the person in it. They may fill in small details that are consistent with it, but they cannot invent a fact that matters, and they cannot forget one that is written down.
That is what cross-examination is built on. If a witness says something on the stand that the affidavit contradicts, or leaves out something it plainly says, the cross-examining attorney can impeach them: read the line back and let the judge see the gap. A witness who knows the affidavit cold gives the other side nothing to work with.
