Struggle to get prisoner on trial (7)
I believe the answer is:
contest
'struggle' is the definition.
(I've seen this in another clue)
'prisoner on trial' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'trial' becomes 'test' (synonyms).
'con'+'test'='CONTEST'
'to get' acts as a link.
(Other definitions for contest that I've seen before include "Competition; dispute" , "Tournament" , "Oppose - competition" , "Competition or conflict" , "Match" .)