In court compassion is resistant to persuasion (6)
I believe the answer is:
uppity
'resistant to persuasion' is the definition.
(uppity means arrogant or obstinate)
'in court compassion' is the wordplay.
'in court' becomes 'up' (up before a judge).
'compassion' becomes 'pity' (synonyms).
'up'+'pity'='UPPITY'
'is' is the link.
(Other definitions for uppity that I've seen before include "Pert; haughty" , "In need of slapping down?" , "Difficult to control" , "Impertinent" , "Not easily persuaded" .)