  9C J1503+4528 is a very young CSS radio galaxy, with an age of order 10^4
years. This source is therefore an ideal laboratory for the study ofthe
intrinsic host galaxy/IGM properties, interactions between the radio source and
surrounding ISM, links between star formation and AGN activity and the radio
source triggering mechanism. Here we present the results of a spectroscopic
analysis of this source, considering each of these aspects of radio source
physics.
  We find that shock ionization by the young radio source is important in the
central regions of the galaxy on scales similar to that of the radio source
itself, whilst evidence for an AGN ionization cone is observed at greater
distances. Line and continuum features require the presence of a young stellar
population, the best-fit model for which implies an age of 5x10^6 years,
significantly older than the radio source.
  Most interestingly, the relative sizes of radio source and extended emission
line region suggest that both AGN and radio source are triggered at
approximately the same time.
  If both the triggering of the radio source activity and the formation of the
young stellar population had the same underlying cause, this source provides a
sequence for the events surrounding the triggering process. We propose that the
AGN activity in 9C J1503+4528 was causedby a relatively minor interaction, and
that a super-massive black hole powering the radio jets must have been in place
before the AGN was triggered.
