  The possibility of a negative drag force on a defect in nonequilibrium
polariton quantum fluids is presented. We relate this phenomenon to the
selective parametric amplification of the waves scattered by the defect. This
leads to the prediction that mobile defects acquire a non-zero velocity with
respect to the polariton nonequilibrium fluid. We derive a direct relation
between the drag force and the momentum distribution of the fluid, that allows
for the experimental verification of our predictions.
