Drive off and swim round the pierhead (5)
I believe the answer is:
repel
'drive off' is the definition.
(synonyms)
'swim round the pierhead' is the wordplay.
'swim' becomes 'reel' (I've seen this before).
'round' indicates putting letters inside.
'the pierhead' becomes 'p' (head letter of 'pier').
'reel' going around 'p' is 'REPEL'.
'and' acts as a link.
(Other definitions for repel that I've seen before include "Fight off - drive back" , "give you the creeps" , "Fend off" , "Deflect" , "Turn away" .)