It is a term first used by NFL announcers to gently describe to the audience that a player had just taken a shot to the nuts.
They would say something like, "ouch, that looked like a tough shot the uh well....that must have hurt. Then another announcer would chime in with yes, that looked like a "GROIN PULL...That can really be painful. The announcers both look flushed and lean forward as if they are going to be hit in the nuts too. The other announcer agrees as the camera pans away to the player who is writhing in pain and rolling on the field.