Gesture of respect abrupt? Certainly back to front! (7)
I believe the answer is:
curtsey
'gesture of respect' is the definition.
(I've seen this in another clue)
'abrupt? certainly back to front' is the wordplay.
'abrupt?' becomes 'curt' (I've seen this before).
'certainly' becomes 'yes' (both can be used to answer in the affirmative).
'back to front' is a reversal indicator.
'yes' backwards is 'sey'.
'curt'+'sey'='CURTSEY'
(Other definitions for curtsey that I've seen before include "old form of obeisance" , "Gesture of respect" , "Girl's bob" , "Formal greeting, bob" , "Respectful greeting" .)