Green’s Dictionary of Slang

casualty n.

a black eye; thus one who suffers such a bruise (see cit. 1885).

[UK]Daily News 21 Mar. in Ware (1909) 66/1: In one of these contests [...] Scott became what is now called a ‘casualty’. He suffered a contusion.
[UK]J. Ware Passing Eng. of the Victorian Era.