Upright holy man behind sentimentality about upset pal (8)
I believe the answer is:
'upright' is the definition.
(goalpost is a kind of upright)
'holy man behind sentimentality about upset pal' is the wordplay.
'holy man' becomes 'st' (**).
'behind' is a charade indicator (letters next to each other).
'sentimentality' becomes 'goo' (informal term for sentimentality).
'about' indicates putting letters inside.
'upset' is an anagram indicator.
'pal' anagrammed gives 'alp'.
'goo' going around 'alp' is 'goalpo'.
'st' put after 'goalpo' is 'GOALPOST'.
(Other definitions for goalpost that I've seen before include "One of four supporters at ends of pitch", "it's unfair to move", "One propping up the bar", "one unfairly moved", "Upright with net attached".)