Injustice fires a nun's storm (10)
I believe the answer is:
Here is my best explanation:
'injustice' is the definition.
('unfairness' can be a synonym of 'injustice')
'fires a nun's storm' is the wordplay.
'storm' indicates an anagram.
'firesanuns' anagrammed gives 'UNFAIRNESS'.
(Other definitions for unfairness that I've seen before include "Inequity", "quality of a brunette might you say?" and "Discrimination".)