Reckless returning to capture American cavalryman (6)
I believe the answer is:
hussar
'cavalryman' is the definition.
(hussar is a kind of cavalryman)
'reckless returning to capture american' is the wordplay.
'reckless' becomes 'rash' ('rash' can be a synonym of 'reckless').
'returning' is a reversal indicator.
'to capture' is an insertion indicator.
'american' becomes 'us'.
'rash' backwards is 'hsar'.
'hsar' going around 'us' is 'HUSSAR'.
(Other definitions for hussar that I've seen before include "Soldier in a light cavalry regiment" , "Cavalryman, originally Hungarian" , "Hungarian soldier" , "one often up on a charge" , "Horseman" .)