Robber boy gets right one (7)
I believe the answer is:
ladrone
'robber' is the definition.
(I've seen this before)
'boy gets right one' is the wordplay.
'boy' becomes 'lad' (informal term for boy).
'gets' means one lot of letters go next to another.
'right' becomes 'r' (common abbreviation).
'lad'+'r'+'one'='LADRONE'
(Other definitions for ladrone that I've seen before include "he'd nip there once" , "robber" , "Old pirate" .)