  Backbone members are recognized as essential parts of an organization, yet
their role and mechanisms of functioning in networks are not fully understood.
In this paper, we propose a new framework called Twotier to analyze the
evolution of community sports organizations (CSOs) and the role of backbone
members. Tier-one establishes a dynamic user interaction network based on
grouping relationships, and weighted k-shell decomposition is used to select
backbone members. We perform community detection and capture the evolution of
two separate sub-networks: one formed by backbone members and the other formed
by other members. In Tier-two, the sub-networks are abstracted, revealing a
core-periphery structure in the organization where backbone members serve as
bridges connecting all parts of the network. Our findings suggest that relying
on backbone members can keep newcomers actively involved in rewarding
activities, while non-rewarding activities solidify relations between backbone
members.
