Top side improperly put down (7)
I believe the answer is:
deposit
'put down' is the definition.
(I've seen this before)
'top side improperly' is the wordplay.
'top side' becomes 'topside' (synonyms).
'improperly' indicates an anagram (I've seen this in other clues).
'topside' with letters rearranged gives 'DEPOSIT'.
(Other definitions for deposit that I've seen before include "Topside (anag) - put down" , "Drop" , "Posited as down payment" , "fur, possibly" , "is one back on the bottle?" .)