Grub rejected by the French ringleader - a housebreaker (7)
I believe the answer is:
burglar
'a housebreaker' is the definition.
(I've seen this before)
'grub rejected by the french ringleader' is the wordplay.
'rejected' says the letters should be written backwards.
'by' means one lot of letters go next to another.
'the french' becomes 'la' ('the' in French).
'ringleader' becomes 'r' (first letter of ring).
'grub' in reverse letter order is 'burg'.
'burg'+'la'+'r'='BURGLAR'
(Other definitions for burglar that I've seen before include "Intruder with intent to steal" , "Thieving intruder" , "Housebreaker" , "He takes" , "Breaker and enterer?" .)