Upset by setter's first clues (4)
I believe the answer is:
tips
'clues' is the definition.
'upset by setter's first' is the wordplay.
'upset' becomes 'tip' (**).
'by' says to put letters next to each other.
'first' indicates taking the first letters.
The first letter of 'setters' is 's'.
'tip'+'s'='TIPS'
(Other definitions for tips that I've seen before include "Areas for dumping waste" , "Hints or gratuities" , "extra payments" , "leavings in restaurant?" , "Ends" .)