Waste of a grill for Shea's bash (5)
I believe the answer is:
ashes
'waste of a grill' is the definition.
(waste left in a fire grill)
'shea's bash' is the wordplay.
'bash' indicates anagramming the letters.
'sheas' with letters rearranged gives 'ASHES'.
'for' is the link.
(Other definitions for ashes that I've seen before include "Cinders - which were once kept in the 3 20 at 18" , "Remains of the Yule logs?" , "Embers" , "Remnants of a fire" , "Burnt residue" .)