blackleg

Short definition from Wiktionary

Noun

1. 1
   A fatal cattle disease caused by the soil-borne bacterium Clostridium chauvoei; symptomatic anthrax.
2. 2
   A disease of potato crops caused by pectolytic bacteria, characterized by blackening and decay of the lower stem portion.
3. 3
   A disease of brassicas caused by the fungus Leptosphaeria maculans
4. 4
   A person who cheats in a game; a cheater, especially a dishonest bookmaker.
5. 5
   A person who takes the place of striking workers.

Verb

1. 1
   To continue working whilst fellow workers strike.