Brief outlines how courts should evaluate evidence of agreement under Section 1 of the Sherman Act.
“Summary judgment is improper if a juror could reasonably infer agreement from just one of the interpretations.”
That single sentence captures why the American Antitrust Institute’s May 26, 2026, amicus curiae brief in a Second Circuit appeal arising from the LIBOR antitrust litigation stands out – and what makes it an authoritative work that plaintiff-side antitrust practitioners should study closely and repeatedly.
It is required reading.
Editor’s Note: An earlier version of this post incorrectly stated the date of the AAI amicus brief and linked to an incorrect document. We corrected the post on June 30, 2026. We regret any confusion this may have caused and appreciate the heads up. Also note that the document itself has the incorrect date on the third page, but it is correct on the final page.
The case itself is one phase in the long‑running LIBOR litigation involving allegations that major global banks coordinated submissions to suppress benchmark interest rates. But what matters here — and what the AAI brief gets exactly right — is how courts are supposed to evaluate evidence of agreement under Section 1 of the Sherman Act.
Collusion is hidden—and the law reflects that reality
The AAI brief starts where antitrust law has always started—with the reality of how conspiracies operate:
“Because collusion is almost always hidden, Section 1 plaintiffs are often forced to rely on circumstantial evidence—including evidence of defendants’ conduct—to prove a violation.”
That is not a fallback position. It is the baseline. Cartels are not documented in neat agreements. They are inferred from conduct, communications, patterns, and context. Courts have long recognized that this is not just permissible, it is inevitable.
The problem begins when courts treat that reality as a weakness rather than a premise.
The mistake: turning tools into requirements
The brief’s most important doctrinal move is a simple one: restoring flexibility.
“Nowhere has this Court or the Supreme Court suggested that independent evidence of an actual agreement ‘must’ be direct evidence.… A plaintiff … ‘may’ rely on the parallel‑plus framework, preserving flexibility to permit proof using independent circumstantial evidence.”
That distinction—may versus must—is significant.
“Parallel‑plus” is not a gatekeeping device. It is one evidentiary path among several. When courts convert it into a rigid framework, they do more than structure analysis—they narrow the range of acceptable proof in ways the law does not require.
Where there is evidence of communications among competitors, or statements indicating coordination, those forms of proof do not need to be forced back into an economic “plus factor” model. They stand on their own.
Documentary antitrust proof: not background, but proof
The strongest part of the AAI brief is its insistence that documentary evidence be treated as what it is: evidence of agreement.
In the LIBOR litigation, plaintiffs identified extensive communications among market participants discussing submissions and acknowledging manipulation. The district court discounted those materials as ambiguous or insufficiently probative. The AAI brief rejects that move.
Statements among competitors—particularly statements describing coordinated behavior—are not just context. They are evidence. Courts err when they:
- treat them as weaker than economic evidence,
- dismiss them because they admit competing interpretations, or
- require plaintiffs to reconstruct agreement exclusively through conduct‑based “plus factors.”
In conspiracy cases, where explicit agreements are rarely memorialized – they can literally be solidified with winks and nods – documentary evidence of communications may be the most direct evidence available. Downgrading it because it requires inference simply misunderstands the evidentiary task.
Antitrust proof and the illusory distinction
The brief also targets a deeper conceptual mistake:
“The distinction between direct and circumstantial evidence … is also illusive… ‘[A]ll evidence depends upon some inferences.’”
That is not merely a rhetorical point; it fixes a basic error in how courts sometimes think about evidence.
Courts sometimes describe “direct evidence” as evidence requiring “no inference.” But that description collapses on contact with reality. Communications require interpretation. Conduct requires context. Even so‑called direct statements are understood through inference.
Once that is recognized, the hierarchy collapses. The question is not whether evidence requires inference. It always does. The question is whether the inference is reasonable.
Matsushita: a standard of reasonableness, not certainty
Nothing in the AAI brief departs from Matsushita v. Zenith. It restores it.
Matsushita limits unreasonable inferences from ambiguous evidence. It does not require plaintiffs to negate every lawful explanation. It does not authorize courts to choose between competing interpretations at summary judgment. And it does not elevate skepticism into a substitute for analysis.
The governing standard is the one the AAI states directly:
“Summary judgment is improper if a juror could reasonably infer agreement from just one of the interpretations.”
That is not permissive. It is the rule.
The real error: courts weighing evidence
The AAI brief identifies the problem with precision: courts are no longer just evaluating whether evidence is sufficient—they are weighing it.
That shift shows up in familiar ways:
- parsing “plus factors” one at a time and discarding each in isolation,
- demanding “same or very similar” conduct instead of recognizing similar effects,
- discounting documentary evidence because it admits competing interpretations, and
- comparing plaintiffs’ evidence against defendants’ competing narratives at the summary judgment stage.
None of those moves tests sufficiency. All of them decide the case.
And once courts move from asking “could a reasonable jury infer agreement?” to asking “which explanation is more persuasive?,” the result is predictable: the jury never gets the case.
Courts must apply standards,
not rewrite them
The AAI’s brief does not attempt to expand antitrust doctrine. It does something more direct—and more necessary. It insists that courts stop rewriting settled standards under the guise of applying them.
Antitrust law has always depended on inference. It has always asked courts to distinguish reasonable conclusions from speculation. But it has never required certainty, and it has never displaced the jury’s role in choosing among competing interpretations of the evidence.
When courts demand that plaintiffs disprove every lawful explanation, or dismiss documentary evidence as mere ambiguity, they do more than misapply precedent, they raise the bar so high that proof of coordinated conduct can rarely clear it.
That is not Matsushita. It is a distortion of it.
The question is not whether inference is required—it always is.
The question is who draws it.
And when courts answer that question for the jury—by parsing evidence into pieces, weighing it against competing explanations, or insisting on near‑certainty—they are not screening cases. They are deciding them.
The opening quote bears repeating.
“Summary judgment is improper if a juror could reasonably infer agreement from just one of the interpretations.”
Edited by Tom Hagy, Editor-in-Chief, Mogin Law Blog. Contact us at Info@MoginLawLLP.com.
Takeaways
- Inference is not a defect. Antitrust conspiracies are usually proven through context, conduct, communications, and reasonable inference.
- Parallel-plus is a tool, not a trap. Courts should not turn one evidentiary method (of assessing antitrust proof) into a rigid requirement that narrows legitimate proof.
- Documents matter. Competitor communications and acknowledgments of coordination are evidence (antitrust proof), not background noise to be discounted.
- Juries draw reasonable inferences. Summary judgment is not the place for courts to choose the most persuasive explanation when a reasonable juror could infer agreement.
If you have questions contact us at Info@MoginLawLLP.com.
Members of the press are encouraged to contact us at Media@MoginLawLLP.com.
FAQ
You should contact a qualified competition law firm that has experience with these types of matters. Getting a high-level assessment of whether you have a potentially actionable antitrust case is a good business practice. Contact Mogin Law LLP if you would like to schedule a consultation.
A business lawyer advising a client harmed by competitor coordination should look for evidence, i.e., antitrust proof, that competitors were not acting independently. Useful evidence may include competitor communications, synchronized pricing or output decisions, unusual market behavior, shared explanations for conduct, or departures from ordinary business incentives. A client does not need a written agreement or “smoking gun” to explore an antitrust claim; coordinated conduct may be proven through circumstantial evidence and reasonable inferences drawn from the full factual record.
When assembling antitrust proof, counsel should look for patterns that make independent action less likely: communications among competitors, pricing or output moves that line up in timing or effect, internal documents acknowledging coordination, or conduct that appears contrary to each firm’s independent economic interest. Counsel should assess those facts as a whole rather than separating and discounting each piece of evidence in isolation, because coordinated conduct is often proven through cumulative circumstantial evidence.
In-house counsel should preserve relevant documents, collect the timeline, and separate facts from assumptions. Emails, chats, meeting notes, pricing records, customer complaints, bid data, and internal reactions may all matter. The legal lesson is that circumstantial evidence is still evidence (antitrust proof). The practical lesson is that the company should not allow important context to disappear before counsel can evaluate it.
In-house counsel should start by building the factual record: who coordinated, what conduct changed, when it changed, and how the company was harmed. Pricing patterns, bidding behavior, customer allocation, benchmark submissions, market communications, and internal documents may all help show that competitors were not acting independently. The practical point is to preserve evidence early and assess the conduct as a whole, because antitrust proof often depends on context, timing, and reasonable inference.