In law school, criminal law teaches that there are two types of conspiracies: a "hub-and-spoke conspiracy" and a "chain conspiracy."
In a hub-and-spoke conspiracy, many parties conspire directly with one "hub" or main party, and do not conspire with each other. As the Court of Appeals for the First Circuit explained:
In a "hub-and-spoke conspiracy," a central mastermind, or "hub," controls numerous "spokes," or secondary co-conspirators. These co-conspirators participate in independent transactions with the individual or group of individuals at the "hub" that collectively further a single, illegal enterprise.
United States v. Newton, 326 F.3d 253, 255 n.2 (1st Cir. 2003).
In practice, prosecutions are usually based on ordinary conspiracies rather than hub-and-spoke conspiracies. The Supreme Court ruled in 1946 that a "rimless" hub-and-spoke conspiracy (one in which the spokes do not know each other) is often a collection of separate, direct conspiracies. Kotteakos v. United States, 328 U.S. 750 (1946). Under this Supreme Court precedent, it is easier to try defendants for an ordinary or chain conspiracy than a hub-and-spoke conspiracy.
However, hub-and-spoke conspiracies are common with respect to sham peer review, whereby one physician can obtain removal of a competitor by misusing peer review at one hospital, and later repeating the bad faith peer review at another hospital.