Detained holding artist's trumpet (6)
I believe the answer is:
herald
'trumpet' is the definition.
(thesaurus)
'detained holding artist's' is the wordplay.
'detained' becomes 'held' (I've seen this before).
'holding' indicates putting letters inside.
'artist' becomes 'RA' (Royal Academician, member of Royal Academy of Arts).
'held' enclosing 'ra' is 'HERALD'.
(Other definitions for herald that I've seen before include "Person who announces important news" , "Usher in; proclaim" , "Announce, presage" , "College of Arms official" , "Harbinger, precursor" .)