A strikebreaker (sometimes pejoratively called a scab, blackleg, bootlicker, blackguard or knobstick) is a person who works despite an ongoing strike.
In continuing to work, or taking jobs at a workplace under current strike, strikebreakers are said to "cross picket lines".
"[5] The European Social Charter of 1961 was the first international agreement to expressly protect the right to strike.
Riddall notes that it may have a racist connotation, as it was used in this way in 1859 in the United Kingdom: "If you dare work we shall consider you as blacks..."[23] Lexicographer Geoffrey Hughes, however, notes that blackleg and scab are both references to disease, as in the blackleg infectious bacterial disease of sheep and cattle caused by Clostridium chauvoei.
The use of the term blackleg for a strikebreaker was, however, previously recorded in 1832 during the trial of special constable George Weddell for killing and slaying Cuthbert Skipsey, a striking pitman, near Chirton, Newcastle-upon-Tyne.
[25] However, the Northumbrian folk song "Blackleg Miner" is believed to originate from the 1844 strike, which would predate Hughes's reference.
David John Douglass claims that the term blackleg has its origins in coal mining, as strikebreakers would often neglect to wash their legs, which would give away that they had been working whilst others had been on strike.