Strike underminer (4)
I believe the answer is:
scab
'strike underminer' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scab that I've seen before include "despicable person" , "Blackleg - sign of injury" , "Crusted sore on cut or wound" , "Strikebreaker; mange" , "Strike-breaker; skin disease in animals" .)