In law, rebuttal is a form of evidence that is presented to contradict or nullify other evidence that has been presented by an adverse party.
Special rules apply to rebuttal. Rebuttal evidence or rebuttal witnesses must be confined solely to the subject matter of the evidence rebutted. New evidence on other subjects may not be brought in rebuttal. However, rebuttal is one of the few vehicles whereby a party may introduce surprise evidence or witnesses. How it works is this: Both sides of a controversy are obliged to declare in advance of trial what witnesses they plan to call, and what each witness is expected to testify to. When either a plaintiff (or prosecutor) or defendant brings direct evidence or testimony which was not anticipated, the other side may be granted a specific opportunity to rebut it. In rebuttal, the rebutting party may generally bring witnesses and evidence which were never declared before, so long as they serve to rebut the prior evidence.