Band will repair the damage (9)
'band will' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'repair the damage' is the wordplay.
'repair' indicates an anagram.
'thedamage' is an anagram of 'MEGADEATH'.
Can you help me to learn more?
(Other definitions for megadeath that I've seen before include "end of civilisation", "Huge human tragedy".)