Unpredictable Clapton perhaps covering Supergrass? (7)
I believe the answer is:
erratic
'unpredictable' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for erratic that I've seen before include "Wandering" , "Shifting, unpredictable" , "Volatile" , "Wild" , "Variable" .)