blackleg:
(plural: ‘blacklegs‘; pronunciation: ‘black…leg’ — for the right pronunciation, please click here)
‘strike’ and ‘to strike’, in this context = the act of workers stopping work as a way of showing their protest, and to stop working in order to show protest or dissatisfaction

a blackleg at cards (hiding a card in her sweater sleeve)
a person who continues to work when other workers are on strike;
(in British usage) a worker who opposes (does not accept) trade unions (workers’ unions);
a strikebreaker;
a scab;
a person who cheats at card games,
e.g.
When the regular workers are on strike, several factories engage blacklegs from other places.
A blackleg is also called a ‘scab’ which, apart form other meanings, is also used to refer to the hardened part on a wound or cut while it is healing.
We seldom invite Mathews to join us in our card game sessions as we all know what a blackleg he is!
“Blackleg” is also used to refer to an infectious bacterial disease in animals and plants.
