  Recent experiments revealed non-Fermi-liquid resistivity in the
unconventional superconductor Sr$_{2}$RuO$_{4}$ when strain pushes one of the
Fermi surfaces close to a van Hove singularity. The origin of this behavior and
whether it can be understood from a picture of well defined quasiparticles is
unclear. We employ a Boltzmann transport analysis beyond the single
relaxation-time approximation based on a single band which undergoes a Lifshitz
transition, where the Fermi surface crosses a van Hove singularity, either due
to uni-axial or epitaxial strain. First analytically investigating impurity
scattering, we clarify the role of the diverging density of states together
with the locally flat band at the point of the Lifshitz transition.
Additionally including electron-electron scattering numerically, we find good
qualitative agreement with resistivity measurements on uni-axially strained
Sr$_{2}$RuO$_{4}$, including the temperature scaling and the temperature
dependence of the resistivity peak. Our results imply that even close to the
Lifshitz transition, a description starting from well-defined quasiparticles
holds. To test the validity of Boltzmann transport theory near a van Hove
singularity, we provide further experimentally accessible parameters, such as
thermal transport, the Seebeck coefficient, and Hall resistivity and compare
different strain scenarios.
