Absent evidence of bad faith, a court can admit an expert rebuttal report that introduces a new theory, in an apparent attempt to provide helpful background information. Allegedly, an abrasive metal cleaning material was left in secondary superheater inlet pendent tubes at a Northeast Utilities station in New Hampshire, and the cleaning material circulated and damaged components. The plaintiffs alleged that the defendant violated the Connecticut Product Liability Act. The defendant moved to strike the expert rebuttal report of Thomas Traubert. Traubert relied on Dr. Khan to compute the minimum steam transport velocities required to carry foreign material. Dr. Khan originally relied on 1.0 feet per second and then produced a new report that changed his result to 6.39 feet per second. Traubert then filed a supplemental report. After the defendant disclosed its experts, the plaintiffs served expert rebuttal reports to dispute, in part, the even distribution theory of one of the defendant's experts and the opinions of several defense experts. The defendant argued that the expert rebuttal reports included theories that could have been provided earlier. Generally, an expert rebuttal should not raise new claims or theories. Although part of Traubert's expert rebuttal report contained new analysis and computations, Traubert aimed to rebut a theory of the defendant's expert and to prove that the defense expert's opinion was based on an incorrect assumption. Although the defendant established prejudice, the parties contemplate another deposition of Traubert and that the plaintiff will be responsible for costs of deposition. The defendant established that Dr. John Cammett's report introduced a new theory, that "shot has a tendency to fracture upon impact." Because this opinion did not rebut the statements of the defendant's experts, it did not qualify as proper rebuttal. The court construed the new theory as an attempt to provide helpful background information. The majority of Dr. Cammett's report qualified as rebuttal and, absent evidence of bad faith, the court denied the defendant's motion to strike Dr. Cammett's expert rebuttal report.