  In this paper, we study the effects of modification of gravity on the problem
of dynamical instability of the spherical relativistic anisotropic interiors.
We have considered non-zero influence of expansion scalar throughout during the
evolutionary phases of spherical geometry that led to the use of fluid
stiffness parameter. The modified hydrostatic equation for the stellar
anisotropic matter distributions is constructed and then solved by using radial
perturbation scheme. Such a differential equation can be further used to obtain
instability constraints at both weak field and post-Newtonian approximations
after considering a particular Harrison-Wheeler equation of state. This
approach allows us to deal with the effects of usual and effective matter
variables on the stability exotic stellar of self-gravitating structures.
