The argument against, try to dispute (7)
I believe the answer is:
contest
'to dispute' is the definition.
(I've seen this in another clue)
'the argument against try' is the wordplay.
'the argument against' becomes 'con' (I've seen this in another clue).
'try' becomes 'test' (test is a kind of try).
'con'+'test'='CONTEST'
(Other definitions for contest that I've seen before include "Tournament" , "Competition or conflict" , "Match" , "Competition; dispute" , "Oppose - competition" .)