Routine is back including drag returning (7)
I believe the answer is:
regular
'routine' is the definition.
('regular' can be similar in meaning to 'routine')
'back including drag returning' is the wordplay.
'back' becomes 'rear' ('rear' can be a synonym of 'back'**).
'including' is an insertion indicator.
'drag' becomes 'lug' (I've seen this in other clues).
'returning' is a reversal indicator.
'lug' reversed gives 'gul'.
'rear' placed around 'gul' is 'REGULAR'.
'is' is the link.
(Other definitions for regular that I've seen before include "Habitual or symmetrical" , "Soldier - uniform" , "In accordance with a fixed order" , "Recurring in a uniform manner, say pulse" , "Happening frequently" .)