  We show that the optical force exerted on a finite size chiral sphere by a
surface plasmon mode has a component along a direction perpendicular to the
plasmon linear momentum. We reveal how this chiral lateral force, pointing in
opposite directions for opposite enantiomers, stems from an angular-to-linear
crossed momentum transfer involving the plasmon transverse spin angular
momentum density and mediated by the chirality of the sphere. Our multipolar
approach allows us discussing the inclusion of the recoil term in the force on
a small sphere taken in the dipolar limit and observing sign inversions of the
lateral chiral force when the size of the sphere increases.
