Regressive way of paying someone, one crossing a line (4)
I believe the answer is:
scab
'one crossing a line' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for scab that I've seen before include "evidence of recent injury" , "Crust on wound, or a blackleg" , "cover" , "Scoundrel" , "work when others are out" .)