Go round quickly and tack, going to south (4)
I believe the answer is:
spin
'go round' is the definition.
(thesaurus)
'tack going to south' is the wordplay.
'tack' becomes 'pin' (I've seen this before).
'going to' is a charade indicator (letters next to each other).
'south' becomes 's' ('S' can be a synonym of 'south').
'pin' put after 's' is 'SPIN'.
'quickly and' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
(Other definitions for spin that I've seen before include "Swirling motion" , "certain doctors initiate?" , "Slant put on news etc" , "Run second leg" , "Give it a whirl" .)