Difficult feature of card game ending in controversy (6)
I believe the answer is:
tricky
'difficult' is the definition.
(similar in meaning)
'feature of card game ending in controversy' is the wordplay.
'feature of card game' becomes 'trick' (term in games like bridge).
'ending in' suggests the final letters.
The final letter of 'controversy' is 'y'.
'trick'+'y'='TRICKY'
(Other definitions for tricky that I've seen before include "Crafty, cunning" , "Crafty; needing skill" , "Awkwardly difficult" , "Not that easy" , "Complicated" .)