Celebrity gets scoundrels upset (4)
I believe the answer is:
star
'celebrity' is the definition.
(I know that star is a type of celebrity)
'scoundrels upset' is the wordplay.
'scoundrels' becomes 'rats' (rat can mean a scoundrel or dishonourable person).
'upset' is a reversal indicator.
'rats' back-to-front is 'STAR'.
'gets' is the link.
(Other definitions for star that I've seen before include "Point of light in the heavens" , "Celebrity's" , "See 5" , "Symbol of excellence" , "Sirius, eg" .)