Reason to propose holding it back (6)
I believe the answer is:
motive
'reason' is the definition.
(I've seen this before)
'propose holding it back' is the wordplay.
'propose' becomes 'move' (moving is a kind of proposing).
'holding' means one lot of letters goes inside another.
'back' shows that the letters should be reversed in order.
'it' backwards is 'ti'.
'move' placed around 'ti' is 'MOTIVE'.
'to' is the link.
(Other definitions for motive that I've seen before include "Reason for doing something, perhaps a crime" , "Reason (for acting)" , "Underlying intention" , "Reason for doing something, say murder" , "Ground" .)