Legal Question in Personal Injury in Maryland

Experts almost always have to be disclosed to the other parties before trial, along with a summary of their opinions. Often the adverse party will then take a deposition of the expert. I understand your question to refer to the testimony of a fact witness. If the expert has been properly disclosed, they would typically be called after a fact witness, either to support that witness or in rebuttal. There are occasions when a party is allowed to call an undisclosed expert to rebut "surprise" testimony that could not have been expected.