  Soft rescattering in hard QCD processes may involve non-perturbative, chiral
symmetry breaking interactions. We find that rescattering which changes the
helicity of the struck quark gives rise to a leading twist single spin
asymmetry in semi-inclusive DIS, the angular dependence of which is the same as
that usually ascribed to the Collins effect.
  We argue that helicity-changing rescattering can contribute also to
$k_\perp$-integrated parton distributions.
