cases on the merits, not by surprise, and not by ambush. After disclosures of witnesses are made, a party can conduct discovery of what those witnesses would say on relevant issues, which in turn informs the party’s judgment about which witnesses it may want to call at trial, either to controvert testimony or to put it in context. Orderly procedure requires timely disclosure so that trial efforts are enhanced and efficient, and the trial process is improved. The late disclosure of witnesses throws a wrench into the machinery of trial. A party might be able to scramble to make up for the delay, but last-minute discovery may disrupt other plans. And if the discovery cutoff has passed, the party cannot conduct discovery without a court order permitting extension. This in turn threatens whether a scheduled trial date is viable. And it impairs the ability of every trial court to manage its docket.
With these considerations in mind, we return to the governing rules. Rule 26 states that “a party must, without awaiting a discovery request, provide to the other parties … the name and, if known, the address and telephone number of each individual likely to have discoverable information.” Fed. R. Civ. P. 26(a)(1)(A) (emphasis added). Compliance with Rule 26’s disclosure requirements is “mandatory.” Repulic of Ecuador v. Mackay, 742 F.3d 860, 865 (9th Cir. 2014).
The rule places the disclosure obligation on a “party.” That another witness has made a passing reference in a deposition to a person with knowledge or responsibilities who could conceivably be a witness does not satisfy a party’s disclosure obligations. An adverse party should not have to guess which undisclosed witnesses may be called to testify. We—and the Advisory Committee on the Federal Rules of
