  The onset of runaway stellar collisions in young star clusters is more likely
to initiate with an encounter between a binary and a third star than between
two single stars. Using the initial conditions of such three-star encounters
from direct $N$-body simulations, we model the resulting interaction by means
of Smoothed Particle Hydrodynamics (SPH). We find that, in the majority of the
cases considered, all three stars merge together, and in such three star
mergers, the hydrodynamic simulations reveal that: (1) mass lost as ejecta can
be a considerable fraction of the total mass in the system (up to $\sim25$%);
(2) due to asymmetric mass loss, the collision product can sometimes receive a
kick velocity that exceeds 10 km/s, large enough to allow the collision product
to escape the core of the cluster; and (3) the energy of the ejected matter can
be large enough (up to $\sim 3\times 10^{50}$ erg) to remove or disturb the
inter cluster gas appreciably.
