A center squeeze is a kind of spoiler effect shared by rules like the two-round system, plurality-with-primaries, and ranked choice voting. In a center squeeze, the majority-preferred and socially optimal candidate is eliminated in favor of a more extreme alternative in an early round, while there are still spoilers. Systems with center squeeze are sometimes called centrifugal ("center-fleeing") because they encourage political polarization.
Candidates focused on appealing to a small base of core supporters can "squeeze" broadly-popular candidates trapped between them out of the race, by splitting the first-preference votes needed to survive earlier rounds. This effect was first predicted by social choice theorists in the 1940s and 50s, and has since been documented in various countries using plurality-style electoral systems.