Spoiling act, rebel's jewellery item (8)
I believe the answer is:
bracelet
'jewellery item' is the definition.
(I've seen this before)
'spoiling act rebel's' is the wordplay.
'spoiling' indicates anagramming the letters.
'act'+'rebel'='actrebel'
'actrebel' with letters rearranged gives 'BRACELET'.
(Other definitions for bracelet that I've seen before include "Ornamental band worn on wrist" , "charm?" , "Might Bel react to the piece of jewellery?" , "Personal ornament" , "Arm band" .)