Against some clever suspect (6)
I believe the answer is:
versus
'against' is the definition.
(as in one sports team versus another)
'some clever suspect' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'VERSUS' can be found hidden inside 'clever suspect'.
(Other definitions for versus that I've seen before include "playing" , "In opposition to" , "taking part in team sports" , "Set against" , "Opposed to" .)