Those in the noble art of fisticuffs? (5)
I believe the answer is:
dukes
'those' is the definition.
I can't tell whether this definition defines the answer.
'noble art of fisticuffs?' is the wordplay.
'noble' becomes 'duke' (duke is a kind of noble).
'art of fisticuffs?' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'duke'+'s'='DUKES'
'in the' is the link.
Can you help me to learn more?
(Other definitions for dukes that I've seen before include "Titled gents or slangy fists" , "Peers of the realm" , "Noblemen" , "eg 21, 22 and Plaza-Toro" .)