From Goodman v. Staples, the Office Superstore, LLC, 2011 U.S. App. LEXIS 8979 (9th Cir. May 3, 2011):

Federal Rule of Civil Procedure 26(a)(2) requires a party to timely disclose a written report of a witness "if the witness is one retained or specially employed to provide expert testimony in the case . . . ." Generally speaking, treating physicians are excused from this requirement. They are a species of percipient witness. They are not specially hired to provide expert testimony; rather, they are hired to treat the patient and may testify to and opine on what they saw and did without the necessity of the proponent of the testimony furnishing a written expert report.

In this case, the plaintiff's treating doctors not only rendered treatment, but after the treatment was concluded, these very same doctors were provided with additional information by plaintiff's counsel and were asked to opine on matters outside the scope of the treatment they rendered. The district court ruled that these physicians would be allowed to testify to the opinions they formed in the course of caring for the patient, but because no Rule 26 expert witness report had been provided, the court precluded the treating doctors from testifying to opinions they formed afterward, opinions solicited from them solely for the purposes of the litigation.

We hold today that when a treating physician morphs into a witness hired to render expert opinions that go beyond the usual scope of a treating doctor's testimony, the proponent of the testimony must comply with Rule 26(a)(2). However, because the law regarding these hybrid experts was not settled, and because treating physicians are usually exempt from Rule 26(a)(2)'s requirements, we exercise our discretion to apply this clarification prospectively. ***

The issue of when, if ever, a treating physician is transformed into an expert offering testimony on matters beyond the treatment rendered, for purposes of Rule 26 disclosures, is an issue of first impression for us. Goodman argues that Rule 26 does not require a written report before a treating physician testifies to virtually anything. In response, Staples acknowledges that written reports may not always be required of treating physicians, but argues that this exception to the written report requirement applies only when the treating physician formed his opinion during the course of treatment. Goodman relies primarily on a decision from the Sixth Circuit in support of her argument that treating physicians do not need to provide written reports. In Fielden v. CSX Transportation, Inc., 482 F.3d 866 (6th Cir. 2007), the Sixth Circuit held that "a report is not required when a treating physician testifies within a permissive core on issues pertaining to treatment, based on what he or she learned through actual treatment and from the plaintiff's records up to and including that treatment." Id. at 871. Staples also relies on Fielden, but as supporting its argument that Rule 26 requires a treating physician to disclose a written report unless evidence shows that the physician formed his opinion during the course of treatment.

We agree with Staples that Fielden does not stand for the proposition that a treating physician never has to disclose an expert report. Id. at 870 (noting the concern that permitting treating physicians to testify in all circumstances without providing expert reports would circumvent the policies underlying Rule 26(a)(2)(B)). Instead, the Fielden court concluded that evidence in the record showed that the physician in question had formed his opinion as to causation during the course of treatment. Id. at 871. Although the court did not elaborate on the type of evidence on which it relied in concluding that the physician formed his opinion during the course of treatment, it did distinguish Fielden from an unpublished Sixth Circuit case where there was "no evidence that the treating physician reached the same conclusions regarding causation at the time he treated the patient." Id. (citing Mohney v. USA Hockey, Inc., 138 F. App'x 804, 811 (6th Cir. 2005)) (internal quotation marks and brackets omitted).

In addition to the Sixth Circuit, other courts hold that Rule 26 requires parties to disclose a treating physician's written report in the absence of some evidence that the physician formed his opinion during the course of treatment. The Seventh Circuit recently held that a treating physician who is offered to provide expert testimony as to the cause of the plaintiff's injury, but who did not make that determination in the course of providing treatment, is required to submit an expert report under Rule 26(a)(2). Meyers v. Nat'l R.R. Passenger Corp., 619 F.3d 729, 734-35 (7th Cir. 2010) (affirming grant of summary judgment where no evidence in the record suggested that plaintiff's doctors considered or determined the cause of his injuries during the course of treatment). The Eighth Circuit goes further, requiring disclosure of a written report any time a party seeks to have a treating physician testify as to the causation of a medical condition, as opposed to merely the existence of the condition. Brooks v. Union Pac. R.R. Co., 620 F.3d 896, 900 (8th Cir. 2010) (affirming grant of summary judgment because, without expert testimony as to causation, plaintiff could not prove an essential element under the Federal Employers Liability Act). District courts within this circuit have limited treating physician testimony to opinions formed during the course of treatment when the party seeking admission of the testimony disclosed no expert report. See, e.g., Durham v. Cnty. of Maui, 729 F. Supp. 2d 1188, 2010 WL 2640117, at *8 (D. Haw. 2010); Armatis v. Owens-Brockway Glass Container, Inc., No. S-08-2538, 2010 U.S. Dist. LEXIS 7995, 2010 WL 148692, at *1 (E.D. Cal. Jan. 14, 2010); J.W. v. City of Oxnard, No. CV 07-06191, 2008 U.S. Dist. LEXIS 91366, 2008 WL 4810298, at *7 (C.D. Cal. Oct. 27, 2008); Vines v. United States, No. 2:05-cv-02370, 2008 U.S. Dist. LEXIS 78002, 2008 WL 4470795, at *3 (E.D. Cal. Oct. 2, 2008); Headley v. Ferro Corp., 630 F. Supp. 2d 1261, 1266-67 (W.D. Wash. 2008).

Today we join those circuits that have addressed the issue and hold that a treating physician is only exempt from Rule 26(a)(2)(B)'s written report requirement to the extent that his opinions were formed during the course of treatment. Goodman specifically retained a number of her treating physicians to render expert testimony beyond the scope of the treatment rendered; indeed, to form their opinions, these doctors reviewed information provided by Goodman's attorney that they hadn't reviewed during the course of treatment. For these reasons, we agree with the district court that those doctors fell outside the scope of the "treating physician" exception insofar as their additional opinions are concerned. Therefore, Rule 26(a)(2)(B) required disclosure of written reports. By failing to provide these reports until long after the deadline for plaintiff's expert disclosures had passed, Goodman failed to comply with Rule 26's disclosure requirements.

When a party fails to make the disclosures required by Rule 26(a), the party is not allowed to use the witness to supply evidence at trial unless it establishes that the failure was substantially justified or is harmless. Fed. R. Civ. P. 37(c)(1); see also Torres v. City of L.A., 548 F.3d 1197, 1212-13 (9th Cir. 2008) (citing Yeti by Molly, Ltd. v. Deckers Outdoor Corp., 259 F.3d 1101, 1106 (9th Cir. 2001)). Although we agree with the district court that Goodman failed to comply with Rule 26(a) when she did not timely disclose expert reports for her medical experts, we must also acknowledge that the law regarding the scope of the "treating physician" exception in the hybrid expert situation was unsettled in this circuit before today. While we do not fault the district court for its ruling limiting Goodman's physicians' testimony, we think that fairness counsels in favor of applying our newly-clarified rule regarding hybrid experts prospectively. Under the circumstances, it would be unjust to allow Goodman's mistake about a previously unsettled point of law to be the coup de grâce to her case. Because we hold, as a matter of discretion, that Goodman should be allowed to rectify her error by disclosing reports for her treating physicians, we reverse the district court's summary judgment ruling on causation.