This is an appeal by the National Football League and 32 separately-owned NFL teams (collectively the “NFL” or the “League”) from an order of the district court issuing an injunction that prohibits the League from continuing to impose a “lockout” of NFL players. Brady v. NFL, No. 11-639, — F.Supp.2d -, 2011 WL 1535240 (D.Minn. Apr. 25, 2011). The named plaintiffs (the “Players”) are nine professional football players and one prospective player who brought an action on behalf of themselves and similarly situated players, alleging that the lockout is a “group boycott” that violates the federal antitrust laws and state contract and tort law. On April 25, 2011, the district court entered an order declaring that “the ‘lockout’ is enjoined.” Two days later, the court denied the League’s motion for a stay of the order pending appeal. Brady v. NFL, No. 11-639, — F.Supp.2d -, 2011 WL 1578580 (D.Minn. Apr. 27, 2011).
The League filed a notice of appeal, moved in this court for a stay of the district court’s order pending appeal, and sought expedited hearing of the appeal. On April 29, 2011, we granted a temporary administrative stay of the district court’s order to allow the court sufficient opportunity to consider the merits of the motion for stay pending appeal. On May 3, 2011, we granted the League’s motion to expedite the appeal, established a briefing schedule, and designated June 3, 2011, as the date for oral argument and submission of the case. For the reasons that follow, we now grant the League’s motion for stay pending appeal.
I.
There is a long history of litigation between the NFL and professional football players, much of which is described in prior opinions of this court and the district court. See, e.g., White v. NFL, 585 F.3d 1129 (8th Cir.2009); White v. NFL, 41 F.3d 402 (8th Cir.1994); Powell v. NFL, 930 F.2d 1293 (8th Cir.1989); Mackey v. NFL, 543 F.2d 606 (8th Cir.1976). For purposes of resolving this motion, an abbreviated summary of the more recent history will suffice. In 1992, a jury rendered a verdict in favor of several players, determining that the League’s limits on the ability of players to move from team to team after their contracts expire violated Section 1 of the Sherman Antitrust Act. McNeil v. NFL, 1992 WL 315292, at *1 (D.Minn. Sept. 10, 1992). Shortly thereafter, several players brought another antitrust action seeking to prevent the League from imposing any restrictions on the movement of players whose contracts expired on February 1,1993. White v. NFL, 822 F.Supp. 1389, 1395 (D.Minn.1993). In February 1993, the League and a class of NFL players entered into a Stipulation and Settlement Agreement to resolve that litigation. The settlement agreement provided that the district court would retain jurisdiction over enforcement of the agreement. See White v. NFL, 836 F.Supp. 1458, 1473 (D.Minn.1993).
*788Later that year, the National Football League Players Association (“NFLPA”), as the exclusive collective bargaining representative of the NFL players, and the NFL Management Council, the multi-employer bargaining unit of the NFL owners, reached a new collective bargaining agreement. The agreement was amended and extended several times, and each time, the enforcement jurisdiction of the district court was retained as part of the agreement. White, 585 F.3d at 1134. In May 2008, however, the NFL exercised its right to opt out of the last two years of the most recent agreement, and both the settlement agreement and the collective bargaining agreement were thus due to expire at 11:59 p.m. on March 11, 2011.
For two years prior to the expiration of the agreements, the Players and the League engaged in negotiations over a new collective bargaining agreement, but they did not resolve their differences. As the expiration date approached, the League indicated that it might use a lockout of the players as a tactic in the bargaining process. See Am. Ship Bldg. Co. v. NLRB, 380 U.S. 300, 301-02, 85 S.Ct. 955, 13 L.Ed.2d 855 (1965). The Players then determined that it would not be in their interest to remain unionized, because the existence of the union would “allow the NFL to impose anticompetitive restrictions with impunity,” Compl. ¶ 54, so they took steps to terminate the NFLPA’s status as their collective bargaining agent as of 4:00 p.m. on March 11. The NFLPA notified the League that as of 4:00 p.m. on March 11, it disclaimed any interest in representing the Players in further negotiations.
Also on March 11, the Players filed their complaint in this action, alleging that the lockout threatened by the League would violate the federal antitrust laws and state contract and tort law. Among other relief, the Players sought a preliminary injunction that would prohibit the League from imposing or continuing the lockout.
On March 12, the League imposed a lockout of the Players. At that point, the League notified players under contract that, among other things, they were not permitted to enter team facilities except in connection with a non-team event or a charitable event, they would not receive compensation or health insurance benefits from their teams, and they were not permitted to play, practice, workout, attend meetings, or consult with team medical or training staff at team facilities. The League also filed an amended unfair labor practice charge with the National Labor Relations Board on March 11, alleging that the NFLPA’s disclaimer was a “sham” and that the combination of a disclaimer by the union and subsequent antitrust litigation was a “ploy and an unlawful subversion of the collective bargaining process.” The League had filed a previous charge in February 2011, alleging that the union failed to confer in good faith during negotiations over a new collective bargaining agreement.
After receiving briefs and affidavits from the parties and hearing oral argument from counsel, the district court entered an order that enjoined the lockout. The court rejected the League’s argument that a federal statute, the Norris-LaGuardia Act, 29 U.S.C. § 101, et seq., deprived the court of jurisdiction to grant injunctive relief, because the court concluded that this is not a case “involving or growing out of a labor dispute” as defined by the Act. The court also rejected the League’s position that it should stay the case, under the doctrine of primary jurisdiction, see Reiter v. Cooper, 507 U.S. 258, 268-69, 113 S.Ct. 1213, 122 L.Ed.2d 604 (1993), pending a decision by the National Labor Relations Board on the League’s unfair labor prac*789tice charges. The court determined that the Players had demonstrated that they were suffering, and would continue to suffer, irreparable harm as a result of the lockout, that the harm to the Players outweighed any harm an injunction would cause the NFL, and that the Players had a fair chance of success on the merits of their lawsuit. On the merits, the court concluded that the non-statutory labor exemption from antitrust liability, see Brown v. Pro Football, Inc., 518 U.S. 231, 116 S.Ct. 2116, 135 L.Ed.2d 521 (1996), does not extend “to protect the labor negotiation tool of a ‘lockout,’ as opposed to a mandatory term of collective bargaining, after a union has disclaimed any further representation of its members.” Brady, — F.Supp.2d at -, 2011 WL 1535240, at *36. For these reasons, the court entered the preliminary injunction.
II.
Federal Rule of Appellate Procedure 8(a) governs the power of a court of appeals to stay an order of a district court pending appeal. Under that Rule, we consider four factors in determining whether to issue a stay: “(1) whether the stay applicant has made a strong showing that he is likely to succeed on the merits; (2) whether the applicant will be irreparably injured absent a stay; (3) whether issuance of the stay will substantially injure the other parties interested in the proceeding; and (4) where the public interest lies.” Hilton v. Braunskill, 481 U.S. 770, 776, 107 S.Ct. 2113, 95 L.Ed.2d 724 (1987). The most important factor is the appellant’s likelihood of success on the merits. Shrink Mo. Gov. PAC v. Adams, 151 F.3d 763, 764 (8th Cir.1998); S & M Constructors, Inc. v. The Foley Co., 959 F.2d 97, 98 (8th Cir.1992). The movant must show that it will suffer irreparable injury unless a stay is granted. Packard Elevator v. ICC, 782 F.2d 112, 115 (8th Cir.1986); cf. James River Flood Control Ass’n v. Watt, 680 F.2d 543, 544 (8th Cir.1982) (per curiam) (granting stay pending appeal after determining that “it appears that the United States may suffer irreparable injury unless this court grants the stay”). Ultimately, we must consider the relative strength of the four factors, “balancing them all.” Fargo Women’s Health Org. v. Schafer, 18 F.3d 526, 538 (8th Cir.1994) (appendix); see also Va. Petroleum Jobbers Ass’n v. Fed. Power Comm’n, 259 F.2d 921, 925 (D.C.Cir.1958) (per curiam) (“[I]njury held insufficient to justify a stay in one case may well be sufficient to justify it in another, where the applicant has demonstrated a higher probability of success on the merits.”); Developments in the Law, Injunctions, 78 Harv. L.Rev. 994, 1056 (1965) (“Clear evidence of irreparable injury should result in a less stringent requirement of certainty of victory; greater certainty of victory should result in a less stringent requirement of proof of irreparable injury.”), quoted in Roland Machinery Co. v. Dresser Indus., Inc., 749 F.2d 380, 388 (7th Cir.1984).
We consider first the League’s likelihood of success on the merits. We do not make a final determination on the merits, but consideration of likely success is unavoidable, for the governing standard “compels us to embark upon such an exercise.” Fargo Women’s Health Org., 18 F.3d at 538.
The Norris-LaGuardia Act limits the jurisdiction of a district court to issue an injunction “in a case involving or growing out of a labor dispute.” 29 U.S.C. § 101. The district court ruled that the Act does not apply here and that it had jurisdiction to enjoin the lockout.
Congress wrote the Act in broad language, in order to take the federal courts “ ‘out of the labor injunction busi*790ness.’ ” Jacksonville Bulk Terminals, Inc. v. Int’l Longshoremen’s Ass’n, 457 U.S. 702, 712, 102 S.Ct. 2672, 73 L.Ed.2d 327 (1982) (emphasis omitted) (quoting Marine Cooks & Stewards v. Panama S.S. Co., 362 U.S. 365, 369, 80 S.Ct. 779, 4 L.Ed.2d 797 (1960)). “No court of the United States shall have jurisdiction to issue any ... temporary or permanent injunction in any case involving or growing out of a labor dispute to prohibit any person or persons participating or interested in such dispute ... from doing, whether singly or in concert,” any of several acts. 29 U.S.C. § 104. One of these acts is “refusing ... to remain in any relation of employment.” 29 U.S.C. § 104(a).
Congress’s definition of a “labor dispute” is expansive: “The term ‘labor dispute’ includes any controversy concerning terms or conditions of employment, or concerning the association or representation of persons in ... seeking to arrange terms or conditions of employment, regardless of whether or not the disputants stand in the proximate relation of employer and employee.” 29 U.S.C. § 113(c). “Congress made the definition broad because it wanted it to be broad.” Order of R.R. Telegraphers v. Chi. & N.W. R.R. Co., 362 U.S. 330, 335-36, 80 S.Ct. 761, 4 L.Ed.2d 774 (1960); see Jacksonville Bulk Terminals, 457 U.S. at 712, 102 S.Ct. 2672 (observing that “the statutory definition itself is extremely broad”).
Congress also explicitly stated the meaning of “involving or growing out of’ a labor dispute. “A case shall be held to involve or grow out of a labor dispute when the case involves persons who are engaged in the same industry, trade, craft, or occupation....” 29 U.S.C. § 113(a). Congress described categories of such disputes in sweeping terms: “[Wjhether such dispute is (1) between one or more employers or associations of employers and one or more employees or associations of employees; ... or when the case involves any conflicting or competing interests in a ‘labor dispute’ [as defined in section 113(c) quoted above] of ‘persons participating or interested’ therein.” Id. A person or association is
participating or interested in a labor dispute if relief is sought against him or it, and if he or it ... is a member ... of any association composed in whole or in part of employers or employees engaged in [the same] industry, trade, craft, or occupation [in which such dispute occurs].
29 U.S.C. § 113(b).
The district court apparently did not question that this case is a “controversy concerning the terms and conditions of employment.” 29 U.S.C. § 113(c). The complaint seeks relief concerning such terms and conditions, and the lawsuit was filed on the same day that the Players’ union discontinued long-term collective bargaining over terms and conditions of employment. The Players argued in the district court that the Norris-LaGuardia Act does not preclude a court from enjoining a group boycott, citing Boise Cascade International, Inc. v. Northern Minnesota Pulpwood Producers Ass’n, 294 F.Supp. 1015 (D.Minn.1968). The district court rejected the Players’ argument, because the dispute enjoined in Boise Cascade “was not a controversy over the terms and conditions of employment, but a dispute over the sale of commodities.... Each of the cases [cited in Boise Cascade ] rejected application of the Norris-LaGuardia Act because the disputes did not concern labor, but the sale of goods.” Brady, — F.Supp.2d at - n. 44, 2011 WL 1535240, at *24 n. 44.
The district court reasoned that this case does not involve or grow out of a labor dispute because the Players no long*791er are represented by a union. See id. at -, 2011 WL 1535240, at *24. We have considerable doubt about this interpretation of the Act. The plain language of the Act states that a case involves or grows out of a labor dispute when it is “between one or more employers or associations of employers and one or more employees or associations of employees.” 29 U.S.C. § 113(a)(1) (emphasis added). The Act does not specify that the employees must be members of a union for the case to involve or grow out of a labor dispute.
The Supreme Court decision most closely on point did not limit the Act to disputes involving a union. In New Negro Alliance v. Sanitary Grocery Co., 303 U.S. 552, 58 S.Ct. 703, 82 L.Ed. 1012 (1938), a company sought an injunction against the New Negro Alliance, “a corporation composed of colored persons, organized for the mutual improvement of its members and the promotion of civic, educational, benevolent, and charitable enterprises.” 303 U.S. at 555, 58 S.Ct. 703. The Alliance allegedly had conspired to picket and boycott one of the company’s grocery stores to pressure the store to employ African-American clerks. The company claimed, among other things, that the Alliance’s acts were “unlawful, [and] constitute^] a conspiracy in restraint of trade.” Id. at 558-59, 58 S.Ct. 703. The district court granted an injunction against the Alliance. The court of appeals affirmed, specifically holding the Norris-LaGuardia Act inapplicable. See 92 F.2d 510, 512-13 (D.C.Cir.1937).
The Supreme Court reversed. Although no labor organization was involved in the dispute, the Court ruled that the definitions in the Act “plainly embrace the controversy which gave rise to the instant suit and classify it as one arising out of a dispute defined as a labor dispute.” 303 U.S. at 560, 58 S.Ct. 703. The Court viewed the dispute as one involving “conflicting or competing interests in a ‘labor dispute’ of ‘persons participating or interested’ therein,” id., and further indicated that the Act also embraces controversies “between employers and employees,” as well as those between “labor unions seeking to represent employees and employers[,] and between persons seeking employment and employers.” Id. at 560-61, 58 S.Ct. 703. The Act’s text and the Supreme Court’s interpretation of it raise serious questions about the district court’s conclusion that the Norris-LaGuardia Act does not prohibit or condition injunctions “absent the present existence of a union.” Brady, — F.Supp.2d at -, 2011 WL 1535240, at *24.
The Act’s prohibition on injunctions, moreover, is not limited to cases “involving” a labor dispute. The Act’s prohibition also covers cases “growing out of’ a labor dispute. For several years, through March 11, 2011, the League and the Players’ union were parties to a collective bargaining agreement. See id. at -, 2011 WL 1535240, at *5-6. For approximately two years, through March 11, the League and Players’ union were engaged in collective bargaining over terms and conditions of employment. See id. at -, 2011 WL 1535240, at *6. When that bargaining failed to produce an agreement on disputed employment terms, and the League’s lockout loomed, the union disclaimed its status as the Players’ representative on March 11, and the Players filed this antitrust action on March 11. See id. at -, 2011 WL 1535240, at *6-7. In this action — filed the same day the union discontinued collective bargaining — the Players seek relief concerning terms and conditions of employment. Given the close temporal and substantive relationship linking this case with the labor dispute between League and the Players’ union, we struggle at this juncture to see why this case is not at least one “growing out of a *792labor dispute” — even under the district court’s view that union involvement is required for a labor dispute.
The Players defend the district court’s decision on an alternative ground that the Norris-LaGuardia Act does not prohibit injunctions against a lockout by an employer. The most apposite authorities support the view that the Act bars injunctions against lockouts by employers. See Chi. Midtown Milk Distribs., Inc. v. Dean Foods Co., 1970 WL 2761, at * 1 (7th Cir. July 9, 1970) (per curiam); Clune v. Publishers’ Ass’n of New York City, 214 F.Supp. 520, 528-29 (S.D.N.Y.), aff'd, 314 F.2d 343, 344 (2d Cir.1963) (mem.) (per curiam); Plumbers & Steamfitters Local 598 v. Morris, 511 F.Supp. 1298, 1311 (E.D.Wash.1981). Because the phrase “remain in any relation of employment” naturally applies to employers as well as employees, we are not inclined to disagree with these decisions. See 29 U.S.C. § 104(a).
The Players suggest that section 104(a) — forbidding a district court to enjoin any person from “refusing ... to remain in any relation of employment”— applies only to injunctions against workers, and exists only to clarify that the Act covers both temporary strikes and permanent cessations of employment. The Players note that the quoted phrase was drawn from Section 20 of the Clayton Act, which “was specifically intended ... ‘to guard the right of workingmen to act together in terminating, if they desire, any relation of employment.’” Local 2750, Lumber & Sawmill Workers Union v. Cole, 663 F.2d 983, 986 n. 5 (9th Cir.1981) (quoting S.Rep. No. 63-698, at 51 (1914)); see also de Arroyo v. Sindicato de Trabajadores Packinghouse, 425 F.2d 281, 291-92 (1st Cir.1970).
Our present view is that this interpretation of the Act is unlikely to prevail. As both the D.C. Circuit and the Second Circuit have observed, although Congress “ ‘was largely concerned with the effect of [federal court] interference on unions, the [Clayton Act] was phrased in an evenhanded fashion to protect employer conduct in labor disputes as well as that of unions.’ ” Brown v. Pro Football Inc., 50 F.3d 1041, 1055 (D.C.Cir.1995) (quoting Nat’l Basketball Ass’n v. Williams, 45 F.3d 684, 689 (2d Cir.1995)), aff'd, 518 U.S. 231, 116 S.Ct. 2116, 135 L.Ed.2d 521 (1996). The Norris-LaGuardia Act retained that evenhanded phrasing by precluding an injunction that prohibits “any persons participating or interested in a labor dispute” from refusing to remain in a relation of employment. 29 U.S.C. § 104(a).*
In sum, we have serious doubts that the district court had jurisdiction to enjoin the League’s lockout, and accordingly conclude that the League has made a strong showing that it is likely to succeed on the merits.
We next consider what injury to the parties is likely to arise from this court’s grant or denial of the motion for a stay, and how the public interest would be affected by this court’s decision on the motion. The Players argue that they are suffering irreparable harm as a result of the lockout, and that the grant of a stay pending appeal would subject them to continuing injury. They contend that even if the court decides this case during the NFL off-season, they are injured irrepara*793bly by an inability to participate in off-season practice and classroom sessions, to learn their teams’ playbooks, to undergo team-supervised medical procedures and evaluations, and to work out at team facilities. They emphasize that nearly 900 players are free agents without contracts, and that the lockout deprives them of a competitive market through which they can pursue their careers. The Players argue that every day of a lockout increases the chance that the 2011 season will be cancelled or significantly shortened, because teams must sign free agents and rookies in order to finalize their rosters. Because the career of a professional football player is typically short, they assert that the loss of even one season of competition is very detrimental.
The League contends that it is irreparably harmed by the district court’s injunction, because its ability to maintain the lockout is essential to the League’s negotiating position in an ongoing dispute with the Players, and that there is no way to measure and compensate the League for its loss of leverage and consequent delay if the injunction is not stayed. See Int’l Ass’n of Bridge, Structural & Ornamental Iron Workers v. Pauly Jail Bldg. Co., 118 F.2d 615, 616-17 (8th Cir.1941) (“The fact must not be lost sight of, that however narrow the scope of injunctive relief may be in form, the issuance of the writ for any purpose in a labor dispute will generally tip the scales of the controversy.”). The NFL observes that this court, in a different context, has recognized irreparable harm based on the impossibility of recreating a negotiating environment that a stay pending appeal was designed to preserve. Iowa Util. Bd. v. FCC, 109 F.3d 418, 425 (8th Cir.1996); see also Dynamic Solutions, Inc. v. Planning & Control, Inc., 646 F.Supp. 1329, 1337 (S.D.N.Y. 1986) (copyright-holder deprived of exclusive use satisfied irreparable harm requirement, because “[t]he monetary worth of that leverage in ... negotiations would be difficult, at best, to determine.”). The League also maintains that player transactions that will occur under the injunction— trades, free agent signings, and roster cuts of players under contract — will cause irreparable harm to the League if the district court’s order is not stayed, because it will be impossible to restore the status quo as of April 25 after contracts are formed and transactions completed during the processing of an appeal.
Both sides raise valid points, and this is a case in which one party or the other likely will suffer some degree of irreparable harm no matter how this court resolves the motion for a stay pending appeal. We do not agree, however, with the district court’s apparent view that the balance of the equities tilts heavily in favor of the Players. The district court gave little or no weight to the harm caused to the League by an injunction issued in the midst of an ongoing dispute over terms and conditions of employment. The court found irreparable harm to the Players because the lockout prevents free agents from negotiating contracts with any team, but gave no weight to harm that would be caused to the League by player transactions that would occur only with an injunction against the lockout. The court gave full weight to affidavit evidence submitted by the Players, although that proof was untested by cross-examination at a hearing. Cf. 29 U.S.C. § 107. The district court’s analysis was conducted without the benefit of knowledge that this appeal will be submitted for decision on a highly expedited schedule — a circumstance that should minimize harm to the Players during the off-season and allow the case to be resolved well before the scheduled beginning of the 2011 season.
*794As to the fourth factor in our analysis, the public interest surely favors some resolution between the parties that will permit professional football to be played in 2011, but in this legal context, we see no reason to differentiate between the public interest and the proper application of the federal law regarding injunctions. In sum, we think the League has met its burden to demonstrate that it likely will suffer some degree of irreparable harm without a stay, and the balance of the equities does not favor the Players so decidedly that it should outweigh our present view about likelihood of success on the merits.
For these reasons, the district court’s order of April 25, 2011, is stayed pending the final disposition of this expedited appeal. The temporary stay imposed by our order of April 29, 2011, is dissolved, and it is replaced by the stay imposed by the terms of this order.
We further observe that even if section 104(a) of the Act were construed to permit an injunction against an employer lockout, there is a serious question whether the district court complied with the procedural requirements of the Act — including to hold a hearing in open court with opportunity for cross-examination — before issuing an injunction. See 29 U.S.C. § 107; cf. Mackey, 543 F.2d at 623.