Chap went down with a cry of pain (6)
I believe the answer is:
fellow
'chap' is the definition.
(both can mean a man)
'went down with a cry of pain' is the wordplay.
'went down' becomes 'fell' (fell over).
'with' is a charade indicator (letters next to each other).
'a cry of pain' becomes 'ow' (exclamation of pain).
'fell'+'ow'='FELLOW'
(Other definitions for fellow that I've seen before include "college type" , "Comrade" , "Informal chap, or member of learned society" , "Neglected child" , "Boy or man" .)