  We study scrambling, an avatar of chaos, in a weakly interacting metal in the
presence of random potential disorder. It is well known that charge and heat
spread via diffusion in such an interacting disordered metal. In contrast, we
show within perturbation theory that chaos spreads in a ballistic fashion. The
squared anticommutator of the electron field operators inherits a light-cone
like growth, arising from an interplay of a growth (Lyapunov) exponent that
scales as the inelastic electron scattering rate and a diffusive piece due to
the presence of disorder. In two spatial dimensions, the Lyapunov exponent is
universally related at weak coupling to the sheet resistivity. We are able to
define an effective temperature-dependent butterfly velocity, a speed limit for
the propagation of quantum information, that is much slower than microscopic
velocities such as the Fermi velocity and that is qualitatively similar to that
of a quantum critical system with a dynamical critical exponent $z > 1$.
