  We report the discovery of phenomena consistent with bad-metal relaxation
dynamics in the metallic regime of an optical-lattice Hubbard model. The
transport lifetime induced by inter-particle scattering for a mass current of
atoms excited by stimulated Raman transitions is measured, and the
corresponding analog of resistivity is inferred. By exploring a range of
temperature, we demonstrate incompatibility with weak-scattering theory and a
key characteristic of bad metals: anomalous resistivity scaling consistent with
$T$-linear behavior. We also observe the onset of two behaviors---incoherent
transport and the approach to the Mott-Ioffe-Regel limit---associated with bad
metals. The interaction and temperature scaling of resistivity are verified to
be consistent with dynamic mean-field theory (DMFT) predictions of a bad metal,
which is associated with the reduction of quasiparticle weight by strong
interactions.
