A more thorough explanation:

The Parker Doctrine, also known as the State-Action Doctrine, is a principle in antitrust law that states that the antitrust laws do not apply to a state's anticompetitive acts or official acts directed by a state.

For example, if a state government creates a law that limits competition in a certain industry, that law would not be subject to antitrust scrutiny under the Parker Doctrine. This is because the state is considered to be acting in its sovereign capacity and is therefore exempt from antitrust laws.

The Parker Doctrine was established in the landmark case of Parker v. Brown in 1943. In this case, the Supreme Court ruled that the Sherman Antitrust Act did not apply to a California law that regulated the price of raisins produced in the state.

Overall, the Parker Doctrine provides an important exception to antitrust laws, allowing states to regulate certain industries without fear of antitrust liability.