Being worn, they may fail to function (4)
I believe the answer is:
duds
'fail to function' is the definition.
I can't judge whether this defines the answer.
'being worn they' is the wordplay.
'being' becomes 'dud' (dud is a kind of being).
'worn they' becomes 's' (I am not sure about this - if you are sure you should believe this answer much more).
'dud'+'s'='DUDS'
'may' is the link.
Can you help me to learn more?
(Other definitions for duds that I've seen before include "Failures; clothes" , "Bombs that fail to explode" , "One assumes them" .)