[judge2020]

> A monopoly is not needed for anti-competitive behavior to be illegal. All that is needed is significant market power.

Have any references where someone was sued for antitrust while having <50% marketshare (of course, using the market determined by the court at the time)? If what you say is true, is the cutoff for antitrust action just "when media outlets report on it long enough to actually be put in sight of regulators/congress"?

[stale2002]

Here is the definition that the government gives.

https://www.ftc.gov/tips-advice/competition-guidance/guide-a...

The cutoff is as follows "Courts do not require a literal monopoly before applying rules for single firm conduct; that term is used as shorthand for a firm with significant and durable market power — that is, the long term ability to raise price or exclude competitors"

If you want statements from a judge, regarding the 50 percent specifically, you can look up the following court cases and read from the primary source.

"See Hayden Publ'g Co., Inc. v. Cox Broad. Corp., 730 F.2d 64, 69 n.7 (2d Cir. 1984) ("[A] party may have monopoly power in a particular market, even though its market share is less than 50%."); Broadway Delivery Corp. v. UPS, 651 F.2d 122, 129 (2d Cir. 1981) ("[W]hen the evidence presents a fair jury issue of monopoly power, the jury should not be told that it must find monopoly power lacking below a specified share."); Yoder Bros., Inc. v. Cal.-Fla. Plant Corp., 537 F.2d, 1347, 1367 n.19 (5th Cir. 1976) (rejecting "a rigid rule requiring 50% of the market for a monopolization offense without regard to any other factors")."

But yes, typically, if a company has less than 50% of a market, anti-trust law does not apply. But the word "typically" does not mean "always". (And Apple has 54% of the US market)

And whether it applies, would defend on "other factors", as according to the quote I linked, and there is a good argument, IMO, that a duopoly would be a reasonable "other factor".

[int_19h]

There were cases like that in the pre-Bork era (i.e. when the courts interpreted the law as people who originally wrote it actually intended). Here's one example:

https://supreme.justia.com/cases/federal/us/370/294/

"In 1955, the date of this merger, Brown was the fourth largest manufacturer in the shoe industry, with sales of approximately 26 million pairs of shoes and assets of over $72,000,000 while Kinney had sales of about 8 million pairs of shoes and assets of about $18,000,000."

And even more relevant:

"Another important factor to consider is the trend toward concentration in the industry. It is true, of course, that the statute prohibits a given merger only if the effect of that merger may be substantially to lessen competition. But the very wording of § 7 requires a prognosis of the probable future effect of the merger.

The existence of a trend toward vertical integration, which the District Court found, is well substantiated by the record. Moreover, the court found a tendency of the acquiring manufacturers to become increasingly important sources of supply for their acquired outlets. The necessary corollary of these trends is the foreclosure of independent manufacturers from markets otherwise open to them. And because these trends are not the product of accident, but are rather the result of deliberate policies of Brown and other leading shoe manufacturers, account must be taken of these facts in order to predict the probable future consequences of this merger. It is against this background of continuing concentration that the present merger must be viewed."