  We address the propagation and hadronization of a struck quark by studying
the gauge invariance of the color-averaged cut quark propagator, and by
relating this to the single inclusive quark fragmentation correlator by means
of new sum rules. Using suitable Wilson lines, we provide a gauge-invariant
definition for the mass of the color-averaged dressed quark and decompose this
into the sum of a current and an interaction-dependent component. The latter,
which we argue is an order parameter for dynamical chiral symmetry breaking,
also appears in the sum rule for the twist-3 $\tilde{E}$ fragmentation
function, providing a specific experimental way to probe the dynamical
generation of mass in Quantum Chromo Dynamics.
