Strike-breaker (4)
I believe the answer is:
scab
'strike-breaker' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for scab that I've seen before include "Derogatory term for a strike-breaker" , "Strike breaker" , "Dried surface of wound" , "Crust that forms on a healing skin wound" , "one works during strike" .)