also jock-strap, "supporter of the male genital organs, used in sports," 1897, with strap (n.) + jock slang for "penis" c.1650-c.1850, probably from Jock, the nickname for John, which was used generically for "common man" from c.1500.
To make one's living in the less glamorous and lucrative reaches of professional sports: He spent a couple of years jockstrapping in the minor leagues (1960s+)