Rebuttal is evidence or arguments introduced to counter, disprove, or contradict the opposing party's evidence or argument, either at trial or in a reply brief. In Wireless Agents, LLC v. Sony, a U.S. district court in Texas stated that, in determining whether an expert witness is offering rebuttal, “the court asks whether he is purporting to contradict or rebut expert opinions offered by [the opposing party] as to a claim or defense as to which [the opposing party] will have the burden of proof at trial; whether his evidence is disclosed as rebuttal evidence on the same subject matter as that identified by [the opposing party] in its Rule 26(a)(2)(B) disclosure; and whether the evidence disclosed as rebuttal evidence is intended solely to contradict or rebut that evidence.” Under Federal Rules of Civil Procedure Rule 26(a)(2)(B), a party must disclose in advance whether evidence is meant to serve as rebuttal evidence.
It can also mean the segment of a trial where the opposing party presents their opposing (rebuttal) evidence or arguments.
[Last updated in December of 2020 by the Wex Definitions Team]