I wrote this because boys asked questions about this issue and nobody bloody answers it.
Learning to buy the right undergarments for your comfort and mobility in sports is vital to your performance on races and matches. It begins with understanding your body.
Here is the closest thing I’ve found to an objectively academic clarification of why crotch space requirements differ from person to person (https://5sizes.wordpress.com/) (WARNING: GRAPHIC IMAGES OF MALE ANATOMY. If you choose to read the articles on the page it is your choice. Don’t complain to me about being offended or your discomfort or insecurities from looking at pictures of penises.) on the issue of why it is hard for athletes to shop for underwear.
Because crotch space requirements differ from person to person even though the waist band is the same. The same model or waist size of trunks or briefs might fit and feel different for each user.
There is a difference in crotch space between undergarments designed originally in US size cuts and Asian size cuts. That’s why I always ask the shop attendants if the original designs were made in US Size cuts, if the garment being sold was made in that original design or adapted for the Asian size. Even then most of the time they aren’t well trained enough to know the actual correct product information, so it’s always necessary to take out a sample of the garment in the size you intend to buy and check the crotch space to see if it’s adequate for your anatomy. Make sure there is enough room for your flaccid penis shaft to rest fully out and not suppressed in it’s natural resting length.
Crotch space is as or if not more important than waist size when picking underwear. There is nothing worse that having your schlong smooshed in tight undies all day.