  The semi-inclusive cross section for producing slow protons in charged
current deep inelastic (anti-) neutrino scattering on protons and neutrons is
calculated as a function of the Bjorken $x$ and the proton momentum. The
standard hadronization models based upon the colour neutralization mechanism
appear to underestimate the rate of slow proton production on hydrogen. The
presence of the virtual mesons (pions) in the nucleon leads to an additional
mechanism for proton production, referred to as spectator process. It is found
that at low proton momenta both mechanisms compete, whereas the spectator
mechanism dominates at very small momenta, while the color neutralization
mechanism dominates at momenta larger than 1-2 \, GeV$/c$. The results of the
calculations are compared with the CERN bubble chamber (BEBC) data. The
spectator model predicts a sharp increase of the semi-inclusive cross section
at small $x$ due to the sea quarks in virtual mesons.
