Led to a rotter being expelled from service (6)
I believe the answer is:
caused
'led to' is the definition.
(I've seen this in another clue)
'a rotter being expelled from service' is the wordplay.
I cannot really understand how this works, but
'a' is found in the answer.
'service' could be 'use' (to be of service is to be of use) and 'use' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for caused that I've seen before include "Gave rise to" , "Made happen" , "Produced as an effect" , "Brought about" .)