  Utilizing the kinematical boost in light-front formalism one can address the
issue of relativistic spin operators in an arbitrary reference frame. In the
gauge $A^+=0$, the interaction dependent transverse spin operators can be
separated into three parts. In analogy with the helicity sum rule, we propose a
transverse spin sum rule. We perform a one loop renormalization of the
transverse spin operator and show that the counterterm needed is the same as
the linear mass counterterm in the light-front QCD Hamiltonian.
