  The evolution of timelike geodesic congruences in a spherically symmetric,
nonstatic, inhomogeneous spacetime representing gravitational collapse of a
massless scalar field is studied. We delineate how initial values of the
expansion, rotation and shear of a congruence, as well as the spacetime
curvature, influence the global behavior and focusing properties of a family of
trajectories. Under specific conditions, the expansion scalar is shown to
exhibit a finite jump (from negative to positive value) before focusing
eventually occurs. This nonmonotonic behavior of the expansion, observed in our
numerical work, is successfully explained through an analysis of the equation
for the expansion. Finally, we bring out the role of the metric parameters
(related to nonstaticity and spatial inhomogeneity), in shaping the overall
behavior of geodesic congruences.
