We prove a global Lorentz estimate for the variable power of the gradients of weak solution to parabolic obstacle problems with p(t,x)-growth over a bounded nonsmooth domain. It is mainly assumed that the variable exponents p(t,x) satisfy a strong type log-Hölder continuity, the associated nonlinearities are merely measurable in the time variable and have small BMO semi-norms in the spatial variables, while the underlying domain is quasiconvex.