Definition of "jockstrap"

With their jock-straps pinching, they slouch to attentionWhile queueing for sarnies at the office canteen.

1972, “Thick As A Brick”, Ian Anderson (lyrics), performed by Jethro Tull

There are many accounts of men, back in the 1970s, work out in nothing but a jockstrap.

2010, Erick Alvarez, Muscle Boys: Gay Gym Culture, Routledge, page 105