  Protostellar outflows crisscross the regions of star cluster formation,
stirring turbulence and altering the evolution of the forming cluster. We model
the stirring of turbulent motions by protostellar outflows, building on an
observation that the scaling law of supersonic turbulence implies a momentum
cascade analogous to the energy cascade in Kolmogorov turbulence. We then
generalize this model to account for a diversity of outflow strengths, and for
outflow collimation, both of which enhance turbulence. For a single value of
its coupling coefficient the model is consistent with turbulence simulations by
Li & Nakamura and, plausibly, with observations of the NGC 1333 cluster-forming
region. Outflow-driven turbulence is strong enough to stall collapse in
cluster-forming regions for several crossing times, relieving the mismatch
between star formation and turbulent decay rates. The predicted line-width-size
scaling implies radial density indices between -1 and -2 for regions supported
by outflow-driven turbulence, with a tendency for steeper profiles in regions
that are more massive or have higher column densities.
