  We develop a model for the weak pion production off the nucleon, which
besides the Delta pole mechanism (weak excitation of the $\Delta(1232)$
resonance and its subsequent decay into $N\pi$), includes also some background
terms required by chiral symmetry. We re-fit the $C_5^A(q^2)$ form factor to
the flux averaged $\nu_\mu p \to \mu^-p\pi^+$ ANL $q^2-$differential cross
section data, finding a substantially smaller contribution of the Delta pole
mechanism than traditionally assumed in the literature. Within this scheme, we
calculate several differential and integrated cross sections, including pion
angular distributions, induced by neutrinos and antineutrinos and driven both
by charged and neutral currents. In all cases we find that the background terms
produce quite significant effects and that they lead to an overall improved
description of the data, as compared to the case where only the Delta pole
mechanism is considered. We also show that the interference between the Delta
pole and the background terms produces parity-violating contributions to the
pion angular differential cross section, which are intimately linked to $T-$odd
correlations in the contraction between the leptonic and hadronic tensors.
However, these latter correlations do not imply a genuine violation of time
reversal invariance because of the existence of strong final state interaction
effects.
