Cockney dukes (5)
I believe the answer is:
fists
'dukes' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for fists that I've seen before include "Doubled up hands" , "Boxer's punchers" , "Fighting tools" , "Dukes" , "Hands with fingers clenched" .)