Discovery From a Dual-Hat Expert

A decision involving a so-called “dual-hat expert” arose out of tragedy.  “This case arises from a flood that swept through Waverly, Tennessee on August 21, 2021 ’killing at least 20 people, including children.’ … Plaintiffs claim that the flood resulted because Defendant allowed debris to clog one of its culverts, which caused millions of gallons of pent-up water to divert over the banks of Trace Creek and into the city.” Rigney v. CSX Transportation, Inc., 2026 WL 2078596 (M.D. Tenn. Jul. 17, 2026).

The discovery issue turned on the roles of plaintiffs’ psychiatric injury expert, Dr. William Newman.  Dr. Newman was a “dual-hat expert” on the issue of negligent infliction of emotional distress (“NIED”).  He was a testifying expert as to some injured people and a non-testifying consultant as to others.

Dr. Newman interviewed “numerous individuals,” but produced only 17 reports.  “The briefing illustrates a stark disagreement about the number of interviews that were conducted. However, the Court need not resolve this dispute to address the merits of Defendant’s motion.”

During six days of depositions, “Newman refused, on the advice of Plaintiff’s counsel, to answer questions related to the interviews he conducted that did not result in a report.”  CSX asserted that it was entitled to any notes Dr. Newman took, regardless of whether he generated a report.

In response, “Plaintiffs assert that Defendant is not entitled to any information generated by Newman for interviews he conducted where no report was generated because the information is not relevant and because he was acting as a consulting expert and thus protected by Federal Rule of Civil Procedure 26(b)(4)(D).”

The court set out the governing standard as follows:

Dual-hat experts are single experts who serve both roles, as non-testifying consulting experts and as testifying experts. In the case of dual-hat experts, only materials generated or considered uniquely in the expert’s role as a consultant are exempt from the broader discovery rules for testifying experts…. If there is any ambiguity regarding the role played by a party’s consultant in reviewing or creating documents, it should be resolved in favor of the party seeking discovery.

Id. at * 2 (cleaned up).

The court’s first step was to examine relevancy—the scope of discovery: “Defendant … weakens its argument by conceding that the information sought merely ‘could be’ relevant…. The Court struggles to see how the information gleaned by Newman during interviews of individuals who do not have a pending claim for [negligent infliction of emotional distress] is relevant to a pending claim or defense.”  The court also rejected the defense theory that the information was relevant to credibility or methodology.

It then turned to the “dual-hat” issue:

Newman serves a dual purpose. He serves as a testifying expert for the 17 Plaintiffs with NIED claims; he also was a consulting expert for Plaintiffs who are not submitting that claim to the jury. As a dual-hat expert, materials generated or considered in his role as a consulting expert are not discoverable. Fed. R. Civ. P. 26(b)(4)(D). Defendant’s argument that Newman considered the information gleaned as part of the interviews at issue when forming his opinions as to the 17 Plaintiffs is unavailing and is contradicted by the record. In his deposition, Newman testified that he did not evaluate any Plaintiff “through the lens of another.”

The court added: “Even assuming that the requested information is relevant, there is no ambiguity in Newman’s role as a consulting expert for Plaintiffs who are not pursuing NIED claims, and Plaintiffs have sufficiently shown that Rule 26(b)(4)(D) applies….  Therefore, Defendant’s only remaining avenue for production would be through a showing of exceptional circumstances. It has failed to do so.”

The court held: “The materials generated by Newman related to individuals who are not pursuing a claim of NIED were generated pursuant to his role as a consultant and are exempt from disclosure. Therefore, the Court finds that Defendant is not entitled to discover his notes, unredacted schedules, or to depose Newman again.”