Finish some golf out of form (5,3)
I believe the answer is:
round off
'form' is the definition.
(rounding off is a kind of forming)
'finish some golf out' is the wordplay.
'some' suggests taking the first letters.
'golf' becomes 'roundof' (round of golf is a kind of golf).
'out' means one lot of letters goes inside another.
The first letter of 'finish' is 'f'.
'f' put into 'roundof' is 'ROUND OFF'.
'of' acts as a link.
(Other definitions for round off that I've seen before include "finish" , "Conclude" .)