  In the paper we present a generalization to Hamiltonian flows on symplectic
manifolds of the estimate proved by Ballmann and Wojtkovski in \cite{BaWoEnGeo}
for the dynamical entropy of the geodesic flow on a compact Riemannian manifold
of nonpositive sectional curvature. Given such a Riemannian manifold $M,$
Ballmann and Wojtkovski proved that the dynamical entropy $h_{\mu}$ of the
geodesic flow on $M$ satisfies the following inequality: $$ h_{\mu} \geq
\int_{SM} \traccia \sqrt{-K(v)} d\mu(v), $$ \noindent where $v$ is a unit
vector in $T_pM$, if $p$ is a point in $M$, $SM$ is the unit tangent bundle on
$M,$ $K(v)$ is defined as $K(v) = \mathcal{R}(\cdot,v)v$, with $\mathcal{R}$
Riemannian curvature of $M$, and $\mu$ is the normalized Liouville measure on
$SM$.
  We consider a symplectic manifold $M$ of dimension $2n$, and a compact
submanifold $N$ of $M,$ given by the regular level set of a Hamiltonian
function on $M$; moreover we consider a smooth Lagrangian distribution of rank
$n-1$ on $N,$ and we assume that the reduced curvature $\hat{R}_z^h$ of the
Hamiltonian vector field $\vec h$ is nonpositive. Then we prove that under
these assumptions the dynamical entropy $h_{\mu}$ of the Hamiltonian flow
w.r.t. the normalized Liouville measure on $N$ satisfies: h_{\mu} \geq \int_N
\traccia \sqrt{-\hat{R}_z^h} d\mu.
