  The discovery of a striking astrophysical laboratory in the cluster of
galaxies Abell 1367 (Sakai et al. 2002) is confirmed with independent imaging
and spectroscopic observations and further investigated in the present
analysis. Two giant and ten dwarf/HII galaxies, members to a group, are
simultaneously undergoing a burst of star formation. Redshift measurements
suggest that the group galaxies are in the process of falling into the cluster
at very high speed. We explore two possible mechanisms that could have
triggered the short-lived stellar burst we are witnessing: the first, internal
to the group itself, via tidal interactions among its members, the hypothesis
favoured by Sakai et al. (2002); the second associated with the high velocity
infall of the group galaxies into the cluster intergalactic medium. We present
evidences in favour and against the two hypotheses.
