Chap originally from America supporting game (5)
I believe the answer is:
rufus
'chap originally' is the definition.
'Rufus' can be an answer for 'chap'. I am unsure of the 'originally' bit.
'from america supporting game' is the wordplay.
'from' becomes 'f' (this could be a standard abbreviation I've not previously seen).
'america' becomes 'us' (abbreviation for the United States).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'game' becomes 'ru' (rugby union).
'f'+'us'='fus'
'fus' put after 'ru' is 'RUFUS'.
(Other definitions for rufus that I've seen before include "one killed in New Forest" , "Name of King William II" , "-- Hound, comedian" , "- Wainwright, US singer" , "chap" .)