What is the sham affidavit rule?

sham affidavit rule should be applied with caution because it is in tension with the principle that the court is not to make credibility determinations when granting or denying summary judgment. In order to trigger the sham affidavit rule, the district court must make a factual determination that the contradiction is a sham, and the inconsistency between a party's deposition testimony and subsequent affidavit must be clear and unambiguous to justify striking the affidavit." Yeager v. Bowlin, 693 F.3d 1076, 1080 (9th Cir. 2012) (citations and internal quotation marks omitted) (first alteration in original).