Free market defense against anti-competitive behavior? One argument against a completely free market economy without "government" oversight is the tendency towards anti-competitive behavior. The argument is that government laws are needed to prevent anti-competitive behavior which could be used to create and solidify monopolies.

A typical example of this is the behavior of liquor distributors in the United States. In the United States it is (or was?) a common practice of liquor distributors to coerce retailers into selling only the brands of liquor that the distributor offered. Distributors carrying the major brands would inspect liquor stores and if they found the store selling any small company's liquor, they would threaten them: "Either stop selling this company's liquor, or else our deal is over and we won't supply you anymore." This is deadly threat, since liquor stores need big brands to stay in business. Because of this, it has been traditionally been difficult for small liquor distillers to survive without a deal with a major distributor.

The same kind of argument was floated at the turn of the century (1900). Oil companies would threaten pipelines: don't carry this small oil company's oil or we will drop you. This type threat caused small oil companies to get frozen out of pipeline distribution networks until legislation basically forced pipelines to carry all oil equally and made it illegal to prefer one company's oil to another.

Is it possible in a totally free market economy to combat anti-competitive behavior or is government regulation the only way to stop it?
Depends on what you mean by 'possible'. The liquor stores in your example could form a union, and collectively bargain with brands. Then if a brand breaks a contract with one of them, they all break the contract. This would greatly disincentivize the brands' strong arm practice.

In my opinion this is unlikely to work (it is very hard to organize), but it is 'possible'.