Foul setter on ship getting high (4,2)
I believe the answer is:
mess up
'foul' is the definition.
(thesaurus)
'setter on ship getting high' is the wordplay.
'setter' becomes 'me' (the setter of the clue).
'on' is a charade indicator (letters next to each other).
'ship' becomes 'ss'.
'getting' is a charade indicator (letters next to each other).
'high' becomes 'up' ('up' is associated in meaning with 'high'**).
'me'+'ss'+'up'='MESS-UP'
(Other definitions for mess up that I've seen before include "Fluff" , "Mishandle a situation" , "Spoil" , "Botch" , "ruin" .)