As the public corruption trial of State Assemblyman Sheldon Silver heads to closing arguments on Monday, the clash in the courtroom has been handled largely by well-staffed government and defense legal teams, each with a wealth of experience in handling corruption cases.

But on Thursday, two unfamiliar lawyers took the stage to try to shape the instructions that the judge will give to the jury before deliberations.

In a case in which no witness testified directly to knowledge of an illegal quid pro quo, how Judge Valerie E. Caproni tells jurors to interpret the evidence as it relates to the law could sway deliberations — a fact certainly not lost on the government or the defense.

The two lawyers had largely disappeared during Mr. Silver’s three-week trial in Federal District Court in Manhattan; James M. McDonald sat quietly at the end of the prosecution table, while Robert K. Kry, a defense lawyer, did not even show up in court.