  Virtually, all existing theoretical works on turbulent poloidal momentum
transport are based on quasilinear theory. Nonlinear poloidal momentum flux -
$\langle \tilde{v}_r \tilde{n} \tilde{v}_{\theta} \rangle$ is universally
neglected. However, in the strong turbulence regime where relative fluctuation
amplitude is no longer small, quasilinear theory is invalid. This is true at
the all-important plasma edge. In this work, nonlinear poloidal momentum flux $
\langle \tilde{v}_r \tilde{n} \tilde{v}_{\theta} \rangle $ in strong
electrostatic turbulence is calculated using Hasegawa-Mima equation, and is
compared with quasilinear poloidal Reynolds stress. A novel property is that
symmetry breaking in fluctuation spectrum is not necessary for a nonlinear
poloidal momentum flux. This is fundamentally different from the quasilinear
Reynold stress. Furthermore, the comparison implies that the poloidal rotation
drive from the radial gradient of nonlinear momentum flux is comparable to that
from the quasilinear Reynolds force. Nonlinear poloidal momentum transport in
strong electrostatic turbulence is thus not negligible for poloidal rotation
drive, and so may be significant to transport barrier formation.
