At my school (40-odd years ago) I never saw a jock - we were made to do PE and games (football, hockey, cricket, tennis) with nothing under our shorts. I think the PE master once recommended buying a jock for support when we reached the age where things were starting to grow, but most of us used to change into our bathing trunks instead (in those days, there was only the 'speedo' style!) and than back into ordinary underwear after the showers.
I'm not a gym person, but I do like jocks, and now have loads. A good source is Jockstrap Central