  It is by now well understood that spin asymmetry in deep inelastic scattering
(DIS) can appear if two things are both present: (i) a chirality flip of the
struck quark; (ii) a nonzero T-odd phase due to its final state interaction. So
far (i) was attributed to a new structure/wave function of the nucleon and (ii)
to some gluon exchanges. We propose a new mechanism utilizing strong vacuum
fluctuations of the gluon field described semiclasically by instantons, and
show that both (i) and (ii) are present. The magnitude of the effect is
estimated using known parameters of the instanton ensemble in the QCD vacuum
and known structure and fragmentation functions, without any new free
parameters. The result agrees in sign and (roughly) in magnitude with the
available data on single particle inclusive DIS. Furthermore, our predictions
uniquely relate effects for longitudinally and transversely polarized targets.
