Invalidate points, blocking gold medal finally (5)
I believe the answer is:
annul
'invalidate' is the definition.
(synonyms)
'points blocking gold medal finally' is the wordplay.
'points' becomes 'nn' (abbreviation for 'north' twice).
'blocking' is an insertion indicator.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'finally' suggests the final letters.
The last letter of 'medal' is 'l'.
'nn' going within 'au' is 'annu'.
'annu'+'l'='ANNUL'
(Other definitions for annul that I've seen before include "Recall" , "Declare (a law) invalid" , "scratch" , "Invalidate" , "Nullify" .)