7 under at St Andrews, in messy place, holding 9 iron, round 4 (5-4)
I believe the answer is:
sixty-five
'7 under at st andrews' is the definition.
(St Andrews is a 72 par golf course)
'messy place holding 9 iron round 4' is the wordplay.
'messy place' becomes 'sty'.
'holding' means one lot of letters goes inside another.
'9' becomes 'ix' (Roman numerals).
'iron round e' becomes 'five' (I am not sure about this - if you are sure you should believe this answer much more).
'sty' placed around 'ix' is 'sixty'.
'sixty'+'five'='SIXTY-FIVE'
'in' is the link.
(Another definition for sixty-five that I've seen is " Five times thirteen".)