Scratch-Back is a slur used to describe Hispanics in a derogatory way. Mexicans (illegals) who crawl under fences, getting their backs scratched up in the process, to get into America.
The word Scratch-Back is a racial slur that has been used historically to degrade and dehumanize hispanics. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to hispanics. If you are unsure about whether or not it is appropriate to use the word Scratch-Back, it is best to err on the side of caution and avoid using it in any situation.