  The chiral quark model combined with unitarity and impact parameter picture
provides simple semiclassical mechanism for generation of the single-spin
asymmetry $A_N$ in the $\pi^0$-production in the polarized proton collisions at
RHIC. We derive its linear $x_F$-dependence in polarized proton fragmentation
region along with the energy and transverse momentum independence at large
$p_T$ values.
