Important to get prohibited report on a group of musicians (3,4)
I believe the answer is:
big band
'musicians' is the definition.
(I've seen this before)
'important to get prohibited report on a group' is the wordplay.
I cannot quite understand how this works, but
'important' could be 'big' (synonyms) and 'big' is located in the answer.
'a' could be 'an' and 'an' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
'of' acts as a link.
Can you help me to learn more?
(Other definitions for big band that I've seen before include "Large group of musicians" , "Large jazz ensemble" , "Dance orchestra of 30s" .)