A structural system is "whole" when all of its parts operate together to construct a coherent, identifiable, self-referential domain of knowledge.
A language (Saussure langue) is a structural system.
A large number of myths which are culturally connected or similar is a structural system.
A sport or a political process or a genre of literature or a writer's lifetime production of a genre of literature can be analyzed as if they were structural systems.
A single baseball game, election, or work of literature are not structural systems in Saussure's sense, but they take their meaning from structural systems in which they participate, usually mythic or linguistic. But they could be structural systems if they were understood to be "A structure of emotive objects so complex and so reliable as to have been taken for great poetry by any past age [that] will never . . . so wane with the waning of human culture as not to be recoverable at least by a willing student" (Wimsatt and Beardsley "Affective" 357). Hmmm...wonder where that hyperlink will take us?