United States v. David Sainz, 933 F.3d 1080

In 2012 David Sainz pleaded guilty to six drug offenses and was sentenced to 188 months (within an advisory Guidelines range of 188–235 months).
Sainz entered a post-conviction cooperation agreement with the government that promised a reduced sentence for substantial assistance and included an express waiver of his right to seek relief under 18 U.S.C. § 3582(c)(2).
The government moved under Rule 35(b) and recommended 151 months; the court ultimately resentenced Sainz to the 120‑month statutory mandatory minimum in October 2014, expressly noting it had considered an imminent two‑level Guidelines reduction (Amendment 782).
After Amendment 782 took effect, Sainz moved under § 3582(c)(2) to reduce his 120‑month sentence based on the lowered Guidelines range (from 188–235 to 151–188).
The district court denied the § 3582(c)(2) motion sua sponte on the ground that Sainz had waived the right to seek § 3582(c)(2) relief, even though the government had not invoked the waiver below.
The Ninth Circuit reversed, holding the district court abused its discretion by raising the waiver sua sponte because the government had waived enforcement of the waiver by not invoking it in the district court.

Issue	Plaintiff's Argument	Defendant's Argument	Held
May a district court sua sponte invoke a defendant’s plea‑agreement waiver of the right to seek § 3582(c)(2) relief when the government did not raise it?	Sainz: The court may not; government’s failure to invoke waiver below forfeits it and the court should not act as government’s advocate.	Government: District court may raise waiver sua sponte, analogous to habeas time‑bar cases where courts may correct obvious defects when the State concedes timeliness.	Court held: No. District court abused its discretion by raising the waiver sua sponte because the government waived enforcement by not invoking it.

United States v. Chaney, 581 F.3d 1123 (9th Cir. 2009) (discusses appellate treatment when government does not invoke plea waiver)
United States v. Dunn, 728 F.3d 1151 (9th Cir. 2013) (standards for reviewing § 3582(c)(2) resentencing decisions)
Lightfoot v. United States, 626 F.3d 1092 (9th Cir. 2010) (district court abuse of discretion standard)
Day v. McDonough, 547 U.S. 198 (2006) (permitting sua sponte invocation of habeas statute of limitations in limited circumstances)
Wood v. Milyard, 566 U.S. 463 (2012) (courts should ordinarily respect deliberate state waiver of timeliness defenses)
United States v. Tercero, 734 F.3d 979 (9th Cir. 2013) (government can implicitly waive a contractual waiver by failing to assert it)
Calderon v. United States, 428 F.3d 928 (10th Cir. 2005) (government bears obligation to raise appeal waivers; silence forfeits enforcement)
Burgess v. United States, 874 F.3d 1292 (11th Cir. 2017) (district court may not sua sponte invoke collateral‑attack waivers under civil‑rules principles)
Greenlaw v. United States, 554 U.S. 237 (2008) (party presentation principle: courts decide issues presented by parties)
United States v. Ono, 72 F.3d 101 (9th Cir. 1995) (characterization of § 3582(c)(2) proceedings as criminal in nature)