Dishonest over ringleaders up in court (7)
I believe the answer is:
corrupt
'dishonest' is the definition.
(similar in meaning)
'over ringleaders up in court' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'ringleaders' becomes 'rr' (two R's - R is the leader of the word 'ring').
'in' means one lot of letters goes inside another.
'court' becomes 'ct' (abbreviation used in road names).
'o'+'rr'+'up'='orrup'
'orrup' going inside 'ct' is 'CORRUPT'.
(Other definitions for corrupt that I've seen before include "Not straight, dishonest" , "Wicked; rotten" , "Lacking in integrity" , "Criminal" , "Dishonest, depraved" .)