The Sherman Antitrust Act regulates tons of different aspects of what businesses may do, and does not apply solely to large monopolies. It's certainly been use

The Sherman Antitrust Act regulates tons of different aspects of what businesses may do, and does not apply solely to large monopolies. It's certainly been used in the past to break up monopolies, but it is also the law which forbids companies of any size from using physical aggression, general intimidation tactics, and similar to collect debt for instance. If I own a lawn-mowing business and you owe me money, I can't go tell your neighbors and family that you're a deadbeat, and that's because of the Sherman Antitrust Act. (Notably, insurance companies are considered 'not commerce' so not regulated under this and medical insurance companies are known to do exactly this sort of thing to intimidate people into paying money they owe.)