Outlaw a musical group who are with it! (6)
I believe the answer is:
bandit
'outlaw' is the definition.
(I know that bandit is a type of outlaw)
'a musical group who are with it' is the wordplay.
'a musical group who are' becomes 'band' (I can't justify this - if you can you should believe this answer much more).
'with' says to put letters next to each other.
'band'+'it'='BANDIT'
Can you help me to learn more?
(Other definitions for bandit that I've seen before include "Violent robber" , "Dan bit the robber badly" , "(One-armed?) outlaw" , "Outlaw, brigand" , "Outlaw, robber" .)