Fighter turning up to register after soldier (8)
I believe the answer is:
pugilist
'fighter' is the definition.
(I know that pugilist is a type of fighter)
'turning up to register after soldier' is the wordplay.
'turning' is a reversal indicator.
'to register' becomes 'list' (listing is a kind of registering).
'after' says to put letters next to each other.
'soldier' becomes 'GI' (term for US soldier).
'up' backwards is 'pu'.
'list' after 'gi' is 'gilist'.
'pu'+'gilist'='PUGILIST'
(Other definitions for pugilist that I've seen before include "A professional boxer" , "Fist fighter" , "Prize fighter" .)