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Federal Rules of Civil Procedure
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Federal Rule of Civil Procedure 37 addresses expert disclosure failures, discovery violations, and potential sanctions in federal litigation. This article explains Rules 37(a), 37(b), and 37(c)(1), expert exclusion, substantial justification and harmlessness, scheduling orders, Rule 26 supplementation, and the distinction between Rule 37 sanctions and Rule 702 admissibility.
Federal Rule of Civil Procedure 37 provides important enforcement mechanisms when a party fails to make required expert disclosures, supplement them when required, or comply with a discovery order. Depending on the type of failure, the court may compel disclosure, exclude expert evidence, award expenses and attorney's fees, or impose other sanctions.
A central provision in expert disclosure disputes is Rule 37(c)(1). If a party fails to provide information or identify a witness as required by Rule 26(a) or Rule 26(e), that party generally may not use the undisclosed information or witness to supply evidence on a motion, at a hearing, or at trial unless the failure was substantially justified or harmless.
The applicable Rule 37 provision depends on the type of failure. Rule 37(a) addresses certain missing or incomplete Rule 26(a) disclosures, Rule 37(c)(1) addresses failures to disclose or supplement under Rule 26(a) or (e), and Rule 37(b) applies to violations of discovery orders.
This guide explains how Rules 37(a), 37(b), and 37(c)(1) apply to expert disclosure failures, how courts may evaluate exclusion and other sanctions, and how parties can manage expert disclosures to reduce avoidable discovery disputes.
Rule 37 often becomes relevant when a party does not satisfy an obligation imposed by Federal Rule of Civil Procedure 26.
Rule 26(a)(2) requires parties to disclose witnesses they may use at trial to present expert evidence under Federal Rules of Evidence 702, 703, or 705. Retained or specially employed testifying experts, along with certain party employees whose duties regularly involve expert testimony, generally must provide a written report.
Rule 26(a)(2)(B) specifies the required information, including the expert's opinions and supporting bases, facts or data considered, qualifications, a list of all other cases in which the expert testified at trial or by deposition during the previous four years, and compensation.
Unless otherwise stipulated or ordered by the court, when a witness is not required to provide a written report, the party's disclosure must state the subject matter of the expert evidence and summarize the facts and opinions the witness is expected to present.
The court's schedule controls expert disclosure timing. If no stipulation or court order applies, Rule 26 requires expert disclosures at least 90 days before the date set for trial or for the case to be ready for trial. Evidence intended solely to contradict or rebut evidence on the same subject matter identified in another party's expert disclosure generally must be disclosed within 30 days after that disclosure.
Federal Rule of Civil Procedure 37 provides important enforcement mechanisms when a party fails to make required expert disclosures, supplement them when required, or comply with a discovery order. Depending on the type of failure, the court may compel disclosure, exclude expert evidence, award expenses and attorney's fees, or impose other sanctions.
A central provision in expert disclosure disputes is Rule 37(c)(1). If a party fails to provide information or identify a witness as required by Rule 26(a) or Rule 26(e), that party generally may not use the undisclosed information or witness to supply evidence on a motion, at a hearing, or at trial unless the failure was substantially justified or harmless.
The applicable Rule 37 provision depends on the type of failure. Rule 37(a) addresses certain missing or incomplete Rule 26(a) disclosures, Rule 37(c)(1) addresses failures to disclose or supplement under Rule 26(a) or (e), and Rule 37(b) applies to violations of discovery orders.
This guide explains how Rules 37(a), 37(b), and 37(c)(1) apply to expert disclosure failures, how courts may evaluate exclusion and other sanctions, and how parties can manage expert disclosures to reduce avoidable discovery disputes.
Rule 37 often becomes relevant when a party does not satisfy an obligation imposed by Federal Rule of Civil Procedure 26.
Rule 26(a)(2) requires parties to disclose witnesses they may use at trial to present expert evidence under Federal Rules of Evidence 702, 703, or 705. Retained or specially employed testifying experts, along with certain party employees whose duties regularly involve expert testimony, generally must provide a written report.
Rule 26(a)(2)(B) specifies the required information, including the expert's opinions and supporting bases, facts or data considered, qualifications, a list of all other cases in which the expert testified at trial or by deposition during the previous four years, and compensation.
Unless otherwise stipulated or ordered by the court, when a witness is not required to provide a written report, the party's disclosure must state the subject matter of the expert evidence and summarize the facts and opinions the witness is expected to present.
The court's schedule controls expert disclosure timing. If no stipulation or court order applies, Rule 26 requires expert disclosures at least 90 days before the date set for trial or for the case to be ready for trial. Evidence intended solely to contradict or rebut evidence on the same subject matter identified in another party's expert disclosure generally must be disclosed within 30 days after that disclosure.
The applicable Rule 37 provision depends on the nature of the disclosure or discovery problem:
Rule 37(a): Applies when a required Rule 26(a) disclosure is missing, evasive, or incomplete. A party may move to compel the disclosure, and expense shifting may apply depending on how the motion is resolved.
Rule 37(c)(1): Applies when information or a witness was not disclosed or supplemented as required by Rule 26(a) or (e). Unless the failure was substantially justified or harmless, the party generally may not use the undisclosed information or witness to supply evidence on a motion, at a hearing, or at trial. Additional sanctions may also be available on motion and after an opportunity to be heard.
Rule 37(b): Applies when a party fails to obey a discovery order. The court may impose further appropriate sanctions, including evidentiary restrictions, expenses, or other sanctions authorized by the rule.
These provisions can apply at different stages of the same discovery dispute. A deficient Rule 26(a) disclosure may lead to a Rule 37(a) motion to compel, while later noncompliance with a resulting discovery order may trigger Rule 37(b).
Rule 37(a) permits a party to move to compel a disclosure required by Rule 26(a), and an evasive or incomplete disclosure is treated as a failure to disclose.
A motion must include a certification that the movant conferred or attempted in good faith to confer with the person or party failing to make the disclosure or discovery in an effort to obtain it without court action. Rule 37(a)(5) also includes expense-shifting provisions, depending on how the motion is resolved.
Rule 37(c)(1) directly addresses failures to provide information or identify witnesses as required by Rule 26(a) or (e). Unless the failure was substantially justified or harmless, the party generally may not use the information or witness to supply evidence on a motion, at a hearing, or at trial.
Expert disclosure problems that may create Rule 37(c)(1) issues include:
Failing to identify an expert witness.
Serving a required expert report after the applicable deadline.
Omitting an opinion or material supporting information from the required disclosure.
Offering an opinion that materially expands beyond what was disclosed.
Failing to make a required Rule 26(e) correction or supplementation.
Attempting to use a later declaration or purported supplement to introduce opinions that should have been timely disclosed.
Whether a later submission is proper supplementation or an untimely new opinion depends on the facts, scheduling orders, local rules, and controlling precedent.
Rule 37(b) addresses failure to obey a court order requiring discovery. Unlike Rule 37(c)(1), it depends on noncompliance with an actual discovery order.
Rule 37(b)(2)(A) allows the court to impose appropriate sanctions, including evidentiary restrictions, treating matters as established, striking pleadings, staying proceedings, dismissal, or default judgment. Under Rule 37(b)(2)(C), instead of or in addition to those sanctions, the court must order the disobedient party, the attorney advising that party, or both to pay the reasonable expenses, including attorney's fees, caused by the failure, unless the failure was substantially justified or other circumstances make an award of expenses unjust.
Rule 37(c)(1) allows an exception when a disclosure failure was substantially justified or harmless, but courts do not apply one nationwide multi-factor test. The analysis therefore depends on controlling circuit precedent.
In Southern States Rack & Fixture, Inc. v. Sherwin-Williams Co., 318 F.3d 592 (4th Cir. 2003), an expert developed a previously undisclosed opinion during trial. The district court excluded the opinion, and the United States Court of Appeals for the Fourth Circuit affirmed.
The Fourth Circuit considered:
Surprise to the opposing party.
The ability to cure the surprise.
Potential disruption of trial.
The importance of the evidence.
The nondisclosing party's explanation.
The court explained that the first four considerations primarily relate to harmlessness, while the explanation for nondisclosure principally relates to substantial justification. It also held that bad faith is not required for exclusion under Rule 37(c)(1).
This five-factor framework is the Fourth Circuit's established approach to determining substantial justification and harmlessness under Rule 37(c)(1), but it is not a universal federal test.
Scheduling orders also play an important role in expert disclosure disputes under Federal Rule of Civil Procedure 16.
Rule 26(a)(2)(D) requires expert disclosures at the times and in the sequence ordered by the court. Rule 16(b) allows scheduling orders to modify disclosure timing, and a schedule may be modified only for good cause and with the judge's consent.
Rule 16(f) separately authorizes sanctions when a party or attorney fails to obey a scheduling or other pretrial order. For that reason, a late expert disclosure should be evaluated against the actual scheduling order and any amendments, not just Rule 26's default deadlines.
Rule 37 and Federal Rule of Evidence 702 address different questions. Rule 37 concerns compliance with disclosure and discovery obligations, while Rule 702 sets the principal requirements for admitting expert testimony.
Under Rule 702, the witness must be qualified as an expert by knowledge, skill, experience, training, or education. The proponent must also demonstrate to the court that it is more likely than not that the requirements of Rule 702(a) through (d) are satisfied. Those requirements address whether the expert's specialized knowledge will help the trier of fact, whether the testimony is based on sufficient facts or data, whether it is the product of reliable principles and methods, and whether the expert's opinion reflects a reliable application of those principles and methods to the facts of the case.
Expert testimony may therefore satisfy Rule 702 yet still face exclusion for a disclosure failure under Rule 37. Conversely, timely disclosure does not establish admissibility under Rule 702.
The party bears the applicable disclosure obligations. Depending on the assignment, a testifying expert may need to keep a clear record of:
Opinions and supporting reasons.
Facts or data considered.
Testing, calculations, models, and material assumptions.
Exhibits supporting or summarizing the analysis.
New information or changes that materially affect an opinion.
Rule 26(e)(1) requires timely supplementation or correction when a party learns that a disclosure is materially incomplete or incorrect and the additional or corrective information has not otherwise been made known during discovery or in writing. Supplementation is also required when ordered by the court.
For experts subject to Rule 26(a)(2)(B), the duty extends to information in the report and information provided during the expert's deposition. Additions or changes must be disclosed by the time the party's Rule 26(a)(3) pretrial disclosures are due.
Rule 26(e) creates an ongoing duty to supplement or correct disclosures when its conditions are met, but whether later material is proper supplementation or an untimely new opinion depends on its substance, timing, the scheduling order, and controlling law.
When a disclosure problem arises, the appropriate response depends on the deficiency, its timing, and the governing court orders.
For the party offering the expert, counsel should consider whether the disclosure requires correction or supplementation and whether any new analysis remains within the opinions already disclosed.
For the opposing party, key questions include whether additional expert discovery is needed, whether the deficiency can be cured, and how the new material affects rebuttal, motion practice, or trial preparation.
Controlling circuit precedent, local rules, scheduling orders, and case-specific discovery orders should be reviewed before assuming that exclusion or another sanction will follow.
Federal Rule of Civil Procedure 37 can lead to different consequences depending on whether the issue involves a deficient disclosure, failure to disclose or supplement, or violation of a discovery order. In expert-intensive litigation, early coordination among counsel and the expert can help identify material changes and reduce disputes over whether opinions were properly disclosed.
Can an expert be excluded for late or incomplete disclosures?
Yes. In federal court, Rule 37(c)(1) can result in exclusion of undisclosed information or a witness unless the failure was substantially justified or harmless.
Does Rule 37(c)(1) require a prior motion to compel?
No. Rule 37(c)(1) can apply directly to a failure to comply with Rule 26(a) or (e). Rule 37(b), by contrast, concerns failure to obey a discovery order.
Can sanctions apply when an expert deadline appears in a scheduling order?
Yes. Expert disclosure timing under Rule 26(a)(2)(D) follows the court's order, and Rule 16(f) separately permits sanctions for failure to obey scheduling or pretrial orders.
Is Rule 37 exclusion the same as a Rule 702 expert challenge?
No. Rule 37 addresses disclosure and discovery compliance. Rule 702 sets the principal admissibility requirements for expert testimony. A case may involve either issue or both.
Can experts supplement reports after disclosure deadlines?
Rule 26(e) requires timely supplementation or correction when its conditions are met, but it does not give a party unrestricted freedom to add opinions that should have been included in the original disclosure. Whether a later submission is proper depends on its substance, timing, the scheduling order, and controlling law.
The applicable Rule 37 provision depends on the nature of the disclosure or discovery problem:
Rule 37(a): Applies when a required Rule 26(a) disclosure is missing, evasive, or incomplete. A party may move to compel the disclosure, and expense shifting may apply depending on how the motion is resolved.
Rule 37(c)(1): Applies when information or a witness was not disclosed or supplemented as required by Rule 26(a) or (e). Unless the failure was substantially justified or harmless, the party generally may not use the undisclosed information or witness to supply evidence on a motion, at a hearing, or at trial. Additional sanctions may also be available on motion and after an opportunity to be heard.
Rule 37(b): Applies when a party fails to obey a discovery order. The court may impose further appropriate sanctions, including evidentiary restrictions, expenses, or other sanctions authorized by the rule.
These provisions can apply at different stages of the same discovery dispute. A deficient Rule 26(a) disclosure may lead to a Rule 37(a) motion to compel, while later noncompliance with a resulting discovery order may trigger Rule 37(b).
Rule 37(a) permits a party to move to compel a disclosure required by Rule 26(a), and an evasive or incomplete disclosure is treated as a failure to disclose.
A motion must include a certification that the movant conferred or attempted in good faith to confer with the person or party failing to make the disclosure or discovery in an effort to obtain it without court action. Rule 37(a)(5) also includes expense-shifting provisions, depending on how the motion is resolved.
Rule 37(c)(1) directly addresses failures to provide information or identify witnesses as required by Rule 26(a) or (e). Unless the failure was substantially justified or harmless, the party generally may not use the information or witness to supply evidence on a motion, at a hearing, or at trial.
Expert disclosure problems that may create Rule 37(c)(1) issues include:
Failing to identify an expert witness.
Serving a required expert report after the applicable deadline.
Omitting an opinion or material supporting information from the required disclosure.
Offering an opinion that materially expands beyond what was disclosed.
Failing to make a required Rule 26(e) correction or supplementation.
Attempting to use a later declaration or purported supplement to introduce opinions that should have been timely disclosed.
Whether a later submission is proper supplementation or an untimely new opinion depends on the facts, scheduling orders, local rules, and controlling precedent.
Rule 37(b) addresses failure to obey a court order requiring discovery. Unlike Rule 37(c)(1), it depends on noncompliance with an actual discovery order.
Rule 37(b)(2)(A) allows the court to impose appropriate sanctions, including evidentiary restrictions, treating matters as established, striking pleadings, staying proceedings, dismissal, or default judgment. Under Rule 37(b)(2)(C), instead of or in addition to those sanctions, the court must order the disobedient party, the attorney advising that party, or both to pay the reasonable expenses, including attorney's fees, caused by the failure, unless the failure was substantially justified or other circumstances make an award of expenses unjust.
Rule 37(c)(1) allows an exception when a disclosure failure was substantially justified or harmless, but courts do not apply one nationwide multi-factor test. The analysis therefore depends on controlling circuit precedent.
In Southern States Rack & Fixture, Inc. v. Sherwin-Williams Co., 318 F.3d 592 (4th Cir. 2003), an expert developed a previously undisclosed opinion during trial. The district court excluded the opinion, and the United States Court of Appeals for the Fourth Circuit affirmed.
The Fourth Circuit considered:
Surprise to the opposing party.
The ability to cure the surprise.
Potential disruption of trial.
The importance of the evidence.
The nondisclosing party's explanation.
The court explained that the first four considerations primarily relate to harmlessness, while the explanation for nondisclosure principally relates to substantial justification. It also held that bad faith is not required for exclusion under Rule 37(c)(1).
This five-factor framework is the Fourth Circuit's established approach to determining substantial justification and harmlessness under Rule 37(c)(1), but it is not a universal federal test.
Scheduling orders also play an important role in expert disclosure disputes under Federal Rule of Civil Procedure 16.
Rule 26(a)(2)(D) requires expert disclosures at the times and in the sequence ordered by the court. Rule 16(b) allows scheduling orders to modify disclosure timing, and a schedule may be modified only for good cause and with the judge's consent.
Rule 16(f) separately authorizes sanctions when a party or attorney fails to obey a scheduling or other pretrial order. For that reason, a late expert disclosure should be evaluated against the actual scheduling order and any amendments, not just Rule 26's default deadlines.
Rule 37 and Federal Rule of Evidence 702 address different questions. Rule 37 concerns compliance with disclosure and discovery obligations, while Rule 702 sets the principal requirements for admitting expert testimony.
Under Rule 702, the witness must be qualified as an expert by knowledge, skill, experience, training, or education. The proponent must also demonstrate to the court that it is more likely than not that the requirements of Rule 702(a) through (d) are satisfied. Those requirements address whether the expert's specialized knowledge will help the trier of fact, whether the testimony is based on sufficient facts or data, whether it is the product of reliable principles and methods, and whether the expert's opinion reflects a reliable application of those principles and methods to the facts of the case.
Expert testimony may therefore satisfy Rule 702 yet still face exclusion for a disclosure failure under Rule 37. Conversely, timely disclosure does not establish admissibility under Rule 702.
The party bears the applicable disclosure obligations. Depending on the assignment, a testifying expert may need to keep a clear record of:
Opinions and supporting reasons.
Facts or data considered.
Testing, calculations, models, and material assumptions.
Exhibits supporting or summarizing the analysis.
New information or changes that materially affect an opinion.
Rule 26(e)(1) requires timely supplementation or correction when a party learns that a disclosure is materially incomplete or incorrect and the additional or corrective information has not otherwise been made known during discovery or in writing. Supplementation is also required when ordered by the court.
For experts subject to Rule 26(a)(2)(B), the duty extends to information in the report and information provided during the expert's deposition. Additions or changes must be disclosed by the time the party's Rule 26(a)(3) pretrial disclosures are due.
Rule 26(e) creates an ongoing duty to supplement or correct disclosures when its conditions are met, but whether later material is proper supplementation or an untimely new opinion depends on its substance, timing, the scheduling order, and controlling law.
When a disclosure problem arises, the appropriate response depends on the deficiency, its timing, and the governing court orders.
For the party offering the expert, counsel should consider whether the disclosure requires correction or supplementation and whether any new analysis remains within the opinions already disclosed.
For the opposing party, key questions include whether additional expert discovery is needed, whether the deficiency can be cured, and how the new material affects rebuttal, motion practice, or trial preparation.
Controlling circuit precedent, local rules, scheduling orders, and case-specific discovery orders should be reviewed before assuming that exclusion or another sanction will follow.
Federal Rule of Civil Procedure 37 can lead to different consequences depending on whether the issue involves a deficient disclosure, failure to disclose or supplement, or violation of a discovery order. In expert-intensive litigation, early coordination among counsel and the expert can help identify material changes and reduce disputes over whether opinions were properly disclosed.
Can an expert be excluded for late or incomplete disclosures?
Yes. In federal court, Rule 37(c)(1) can result in exclusion of undisclosed information or a witness unless the failure was substantially justified or harmless.
Does Rule 37(c)(1) require a prior motion to compel?
No. Rule 37(c)(1) can apply directly to a failure to comply with Rule 26(a) or (e). Rule 37(b), by contrast, concerns failure to obey a discovery order.
Can sanctions apply when an expert deadline appears in a scheduling order?
Yes. Expert disclosure timing under Rule 26(a)(2)(D) follows the court's order, and Rule 16(f) separately permits sanctions for failure to obey scheduling or pretrial orders.
Is Rule 37 exclusion the same as a Rule 702 expert challenge?
No. Rule 37 addresses disclosure and discovery compliance. Rule 702 sets the principal admissibility requirements for expert testimony. A case may involve either issue or both.
Can experts supplement reports after disclosure deadlines?
Rule 26(e) requires timely supplementation or correction when its conditions are met, but it does not give a party unrestricted freedom to add opinions that should have been included in the original disclosure. Whether a later submission is proper depends on its substance, timing, the scheduling order, and controlling law.
Federal Rules of Civil Procedure
Federal Rules of Civil Procedure