Fed.R.Civ.P. 50(b) provides:

Renewing the Motion After Trial; Alternative Motion for a New Trial. If the court does not grant a motion for judgment as a matter of law made under Rule 50(a), the court is considered to have submitted the action to the jury subject to the court’s later deciding the legal questions raised by the motion. No later than 10 days after the entry of judgment — or if the motion addresses a jury issue not decided by a verdict, no later than 10 days after the jury was discharged — the movant may file a renewed motion for judgment as a matter of law and may include an alternative or joint request for a new trial under Rule 59. In ruling on the renewed motion, the court may:

(1) allow judgment on the verdict, if the jury returned a verdict;

(2) order a new trial; or

(3) direct the entry of judgment as a matter of law.

From Kelley v. City of Albuquerque, 2008 U.S. App. LEXIS 19706 (10th Cir. Sept. 17, 2008):

The Supreme Court has declared that a "failure to comply with Rule 50(b) forecloses [a party's] challenge to the sufficiency of the evidence." Unitherm Food Sys., Inc. v. Swift-Eckrich, Inc., 546 U.S. 394, 404, 407 (2006). "[T]he precise subject matter of a party's Rule 50(a) motion--namely, its entitlement to judgment as a matter of law--cannot be appealed unless that motion is renewed pursuant to Rule 50(b)." Id. at 404.

[Footnote 15:] Unitherm stressed the mandatory nature of Rule 50(b) by repeatedly warning that a party's failure to file a Rule 50(b) motion left the appellate courts "powerless" to enter judgment in its favor. See, e.g., 546 U.S. at 405. At least one of our sister circuits has read this strong language regarding power as indicating that the a party's failure to file a Rule 50(b) motion deprives an appellate court of subject matter jurisdiction to review the sufficiency of the evidence. See Allison v. City of E. Lansing, 484 F.3d 874, 876 (6th Cir. 2007) ("Given Unitherm Food's holding, it is now clear that renewing the motion post-verdict is jurisdictional and cannot be waived."). The Sixth Circuit's view is open to question because of the Supreme Court's subsequent decision in Bowles v. Russell, 551 U.S. , 127 S. Ct. 2360, 2365 (2007). The Court in Bowles concluded that Federal Rule of Appellate Procedure 4(a) is jurisdictional because it implements 28 U.S.C. § 2107. Id. at 2365-66. We have interpreted Bowles to mean that only rules that implement statutory limits can be jurisdictional. United States v. Mitchell, 518 F.3d 740, 744 (10th Cir. 2008) ("Bowles . . . clarified that court-issued federal procedural rules not derived from statutes are not jurisdictional, but rather inflexible claim-processing rules.")***. Rule 50(b) is not grounded in a statute. Accordingly, in a jurisdictional inquiry relating to it, the principles of Bowles would seemingly be implicated. However, we need not definitively decide this jurisdictional question — a matter of first impression — here. Therefore, we do not do so. Although "a federal court generally may not rule on the merits of a case without first determining that it has jurisdiction," the Supreme Court has recognized that "jurisdiction is vital only if the court proposes to issue a judgment on the merits." Sinochem Int'l Co. v. Malay. Int'l Shipping Corp., 127 S. Ct. 1184, 1191-92 (2007) (alteration and internal quotation marks omitted)***. In denying the City an audience on its causation challenge under the rationale of Unitherm, we need not rule on the merits. Furthermore, we find additional support for a Unitherm-based resolution in our observation that employing Unitherm arguably is a "less burdensome course" than resolving the first-impression jurisdictional question, especially if that resolution potentially would cause us to part company with the Sixth Circuit. *** Accordingly, we need not (and do not) decide here whether a party's failure to file a Rule 50(b) motion deprives us of jurisdiction over its sufficiency-of-the-evidence challenge.