A convict turned up and tricked a knight (7)
I believe the answer is:
galahad
'a knight' is the definition.
(Arthurian knight)
'a convict turned up and tricked' is the wordplay.
'convict' becomes 'lag' (I've seen this before).
'turned up' is a reversal indicator.
'and' means one lot of letters go next to another.
'tricked' becomes 'had' (to have someone can mean to trick them).
'a'+'lag'='alag'
'alag' written backwards gives 'gala'.
'gala'+'had'='GALAHAD'
(Other definitions for galahad that I've seen before include "principled chap" , "Errant fellow" , "extremely honourable man" , "One of Arthur's knights" , "Round Table knight of immaculate purity" .)