Pearls cast before swine ultimately causing setback (7)
I believe the answer is:
relapse
'setback' is the definition.
(I've seen this before)
'pearls cast before swine ultimately' is the wordplay.
'cast' indicates anagramming the letters (letters are dispersed or cast around).
'before' says to put letters next to each other.
'ultimately' indicates one should take the final letters.
The final letter of 'swine' is 'e'.
'pearls' with letters rearranged gives 'relaps'.
'relaps'+'e'='RELAPSE'
'causing' is the link.
(Other definitions for relapse that I've seen before include "Fall ill again after rallying" , "Worsen" , "Unexpected deterioration" , "Return to sickness" , "Sink back into illness" .)