In under par, but missing one's original place (8)
I believe the answer is:
homesick
'missing one's original place' is the definition.
(missing one's home)
'in under par' is the wordplay.
'in' becomes 'home' ('he's in' can mean 'he's home').
'under par' becomes 'sick' (under par can mean sick or unwell).
'home'+'sick'='HOMESICK'
'but' acts as a link.
(Other definitions for homesick that I've seen before include "Missing one's normal environment" , "Unhappy away" , "Nostalgic" , "Feeling sadness when away from family etc" , "I shock me (anag.)" .)