Ring fighter to study enlisted men (8)
I believe the answer is:
toreador
'ring fighter' is the definition.
(I've seen this before)
'to study enlisted men' is the wordplay.
'study' becomes 'read' (synonyms).
'enlisted men' becomes 'OR' (military abbreviation for Other Ranks).
'to'+'read'+'or'='TOREADOR'
(Other definitions for toreador that I've seen before include "A bullfighter, especially on horseback" , "Killer facing charges" , "One who fights bulls" , "He wears a flashy suit" , "Man honoured to be given an ear" .)