  The strongly correlated insulator Ca$_{2}$RuO$_4$ is considered as a
paradigmatic realization of both spin-orbital physics and a band-Mott
insulating phase, characterized by orbitally selective coexistence of a band
and a Mott gap. We present a high-resolution oxygen $K$-edge resonant inelastic
X-ray scattering study of the antiferromagnetic Mott insulating state of
Ca$_{2}$RuO$_4$. A set of low-energy ($\sim$80 and 400 meV) and high-energy
($\sim$1.3 and 2.2 eV) excitations are reported that show strong incident light
polarization dependence. Our results strongly support a spin-orbit coupled
band-Mott scenario and explore in detail the nature of its exotic excitations.
Guided by theoretical modelling, we interpret the low-energy excitations as a
result of composite spin-orbital excitations. Their nature unveil the intricate
interplay of crystal-field splitting and spin-orbit coupling in the band-Mott
scenario. The high-energy excitations correspond to intra-atomic
singlet-triplet transitions at an energy scale set by the Hund's coupling. Our
findings give a unifying picture of the spin and orbital excitations in the
band-Mott insulator Ca$_{2}$RuO$_4$.
