Antitrust Law

Chapter 11

PetPals moves to acquire NatureBowl Inc., its largest regional competitor. The Hart-Scott-Rodino filing goes in and the waiting period begins. Then the FTC issues a second request, a signal that the combined company’s market share in the premium dry dog food segment has caught the agency’s attention. Noodle briefs the board on the 2023 Merger Guidelines and the structural presumption their numbers trigger. PetPals has to decide whether to fight, negotiate a consent decree, or walk away from the deal entirely.

Sherman Antitrust Act

The foundational federal antitrust statute of 1890. Section 1 prohibits contracts, combinations, and conspiracies that unreasonably restrain trade, and Section 2 prohibits monopolization and attempts to monopolize. The Act does not punish size or success earned through better products; it targets the abuse of market power and coordination among competitors.

Clayton Act

The 1914 statute that reaches specific anticompetitive practices before they ripen into Sherman Act violations. Section 7 prohibits mergers and acquisitions whose effect may be substantially to lessen competition or tend to create a monopoly, and it is the legal basis for federal merger review.

Per Se Violations

Categories of conduct so harmful and so lacking in any procompetitive justification that courts declare them illegal without analyzing their actual effects. Horizontal price fixing, market allocation among competitors, bid rigging, and group boycotts are the classic examples.

Rule of Reason

The analysis applied to most conduct outside the per se categories, in which a court weighs the anticompetitive effects of a practice against its procompetitive justifications in the full market context. It is fact intensive and requires defining the market, assessing market power, and evaluating real competitive effects. Merger cases are analyzed this way, informed by the Merger Guidelines.

Relevant Market

The starting point of nearly every antitrust analysis, with two dimensions: the product market, meaning which products consumers treat as substitutes, and the geographic market, meaning where the competition takes place. A firm’s share, and therefore its market power, depends entirely on how the boundary is drawn, so defendants argue for broad markets and enforcers for narrow ones.

Market Concentration and HHI

Concentration measures how much of a market a few firms control. The Herfindahl-Hirschman Index sums the squares of each competitor’s market share, and the 2023 Merger Guidelines treat a post-merger HHI above 1,800 as highly concentrated and an increase of more than 100 points as presumptively concerning. The thresholds do not block a merger by themselves, but they set the presumption the parties must overcome.

Structural Presumption

The rule that a merger creating a highly concentrated market, or significantly increasing concentration in one, is presumed anticompetitive. The burden shifts to the merging parties to show that the numbers overstate the harm, for example because entry is easy, the acquired firm is failing, or the merger produces efficiencies that reach consumers.

Hart-Scott-Rodino Act

The 1976 statute requiring parties to mergers above annually adjusted financial thresholds to notify the FTC and the Department of Justice before closing and to wait while the agencies review the deal. A second request for documents extends the waiting period and signals serious concern. Premerger notification is the procedural gateway through which every significant merger review passes.

Part 1: Find and Research a Proposed Merger

Using the FTC’s Merger Review page, the Department of Justice’s case filings, or recent business news, find a proposed or in-progress corporate merger that interests you. It does not need to be famous, and a merger still pending or under review is often more interesting than a closed one because the outcome is unknown. Once you have selected your merger, use the Antitrust Foundation Builder to walk through the core antitrust concepts and the 2023 Merger Guidelines framework. Then use the Merger Explainer to work through the merger itself, identifying the relevant market, estimating what the deal means for concentration, and assessing where it stands relative to the Guidelines. Verify what the AI tells you against real sources, because market share figures and regulatory status must be confirmed through news coverage, company filings, or agency announcements before you rely on them.

Part 2: Explain It to a Layperson

After completing your research, explain your merger to a friend or family member who has no background in business law, whether in person, by phone, or by text. Try to explain in plain language what the two companies do, why they want to merge, what antitrust law is, why this particular merger might or might not raise legal concerns, and where things currently stand with regulators. Use the Plain Language Coach to prepare for the conversation and to debrief afterward.

Part 3: Post Your Deliverables

After the conversation, write a journal entry of at least 300 words reflecting on the full experience: the research, the explanation, and what both revealed about your understanding of antitrust law. Address three things. First, describe your merger and where it stands relative to the 2023 Merger Guidelines, including whether the concentration math suggests regulatory concern. Second, reflect on the explanation itself: what was hard to explain, what surprised your listener, and what questions they asked that you could not answer cleanly. Third, reflect on what this activity taught you about antitrust law that reading alone would not have. Create a single new discussion thread and post your journal.

Part 4: Share Chat Link

Include one AI chat link with a 1–2 sentence explanation of what the conversation shows and why you chose to share it.

Antitrust Foundation Builder

Act as an expert antitrust law professor teaching a college-level business law survey course. I need to build a working understanding of U.S. antitrust law and the 2023 Merger Guidelines before I apply them to a real merger. Begin with the three foundational federal antitrust statutes, the Sherman Act, the Clayton Act, and the FTC Act, and explain what each one prohibits and why it exists. Then explain the distinction between per se violations and rule of reason analysis, using concrete examples of each. After that, explain how market definition works in antitrust analysis, covering both the product market and the geographic market. Finally, walk me through the key analytical framework of the 2023 Merger Guidelines, focusing on Guidelines 1, 2, and 6, and tell me where in the Guidelines each point appears so I can read it myself. Write in clear paragraph form throughout and keep the language accessible.

A map with page references. The statutes, the two modes of analysis, market definition, and the Guidelines are the four things you need before touching a real deal, and asking where each point appears in the Guidelines lets you read the source rather than trust the summary.

Merger Explainer

Act as a knowledgeable but plain-spoken antitrust advisor helping a college student make sense of a proposed corporate merger. I am going to describe the merger I have been researching, including who the companies are, what they do, what market they compete in, and what I have found about the regulatory status of the deal. After I share what I know, help me answer four questions in plain, accessible language. First, how would antitrust lawyers define the relevant product and geographic market? Second, what does the market concentration picture look like under the HHI structural presumption? Third, based on where the deal currently stands with the agencies, what does that tell us about how merger review actually works? Fourth, in simple terms, is this a deal that raises genuine antitrust concerns, and why or why not? Any market share or concentration number you use must be labeled as either something I provided or an estimate of yours, and tell me what source I should check to confirm it. Ask me to share my merger details to begin.

Four questions and labeled numbers. The questions track the Guidelines’ own analysis, and requiring the AI to distinguish your figures from its estimates is what keeps invented market shares out of your journal.

Plain Language Coach

Act as a communication coach helping a college student explain a complex legal topic to someone with no background in law or business. I am preparing to explain a proposed corporate merger and basic antitrust law to a friend or family member who has never encountered these concepts before. Help me in two ways. First, before the conversation, ask me to describe my merger, then help me build a simple, jargon-free explanation I could actually say out loud to someone unfamiliar with terms like HHI or structural presumption, including plain-language analogies. Second, after I have had the conversation, ask me how it went: what was hard to explain, what questions came up that I could not answer well, and what surprised me. Once I share that debrief, help me identify what the gaps in my explanation reveal about my own understanding.

Teaching as a test of understanding. You cannot explain what you do not understand, and the debrief turns the questions your listener asked into a diagnosis of what you still need to learn.