Court error (4)
I believe the answer is:
foul
'court error' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for foul that I've seen before include "Offensive, abominable" , "Repulsive" , "Putrid" , "Abominable - offence on football field" , "Illegitimate tackle" .)