Rival is excited about case (6)
I believe the answer is:
valise
'case' is the definition.
(valise is a kind of case)
'rival is excited about' is the wordplay.
'about' indicates a hidden word (the clue goes around or about the answer).
'VALISE' can be found hidden inside 'rival is excited'.
(Other definitions for valise that I've seen before include "Travel bag" , "Small piece of luggage" , "Small travelling bag or suitcase" , "Small overnight bag" , "Elvis A? (anag)" .)