States opposed to dropping behind (5)
I believe the answer is:
avers
'states' is the definition.
(to aver is to declare or state)
'opposed to dropping behind' is the wordplay.
'opposed to' becomes 'averse' (I've seen this in another clue).
'dropping behind' means to remove the last letter (the word's back or behind is dropped).
'averse' with its last letter taken off is 'AVERS'.
(Other definitions for avers that I've seen before include "States firmly - really raves" , "States positively" , "Alleges, asserts" , "States to be true" , "Declares to be true" .)