  At leading twist the transverse-momentum dependent parton distributions of
the pion consist of two functions, the unpolarized $f_{1,\pi}(x,\boldsymbol
k^{\, 2}_\perp)$ and the Boer-Mulders function $h_{1,\pi}^{\perp}(x,\boldsymbol
k^{\, 2}_\perp)$. We study both functions within a light-front constituent
model of the pion, comparing the results with different pion models and the
corresponding nucleon distributions from a light-front constituent model. After
evolution from the model scale to the relevant experimental scales, the results
for the collinear pion valence parton distribution function $f_{1,\pi}(x)$ are
in very good agreement with available parameterizations. Using the light-front
constituent model results for the Boer-Mulders functions of the pion and
nucleon, we calculate the coefficient $\nu$ in the angular distribution of
Drell-Yan dileptons produced in pion-nucleus scattering, which is responsible
for the violation of the Lam-Tung relation. We find a good agreement with data,
and carefully discuss the range of applicability of our approach.
