Back regular outsiders? (4)
I believe the answer is:
rear
'back' is the definition.
(something's rear is its back)
'regular outsiders?' is the wordplay.
'outsiders?' says to hollow out the word (remove centre letters) (I've seen 'outsiders' mean this (only the letters on the outside of the word remain)).
'regular' with its middle taken out is 'REAR'.
(Other definitions for rear that I've seen before include "Bring up and care for" , "Bring up (children)" , "what can be brought up, finally" , "Of horse, rise up on hind legs" , "early, long before now" .)