Technically, No
Brief-lined shorts are designed so you don’t need to wear underwear with them.
However, if you’re not comfortable with that, either socially or physically, then you can wear underwear underneath them.
Exceptions
Personally, there are some brief-lined shorts that I do wear underwear with, while others I don’t need to. For example, the Nike Trail Second Sunrise shorts chaff around my groin, and even after a few runs, I can’t get used to the jockey style brief lining. Due to this, I need to wear compression shorts underneath to prevent the excessive rubbing and make them usable.
Meanwhile, the Nathan Front Runner 3.0 shorts had a wonderful boxer brief-style lining, and these were so much nicer to run in at first. Eventually though, due to where the stitches are, these rubbed even worse. So much so that it removed skin and made me bleed on two different occasions. To use these required me to wear compression shorts underneath as well.
Expectations
Thankfully though, the Nike Strides also come in a boxer style brief-lining and don’t chaff. This is what I expected when I first heard and tried brief-lined running shorts. An awesome combination that creates lighter, more comfortable running shorts.
These shorts have become my favorite, default running shorts. Even though it took a few tries to find a pair of brief-lined shorts that work for me, now I don’t want to run without them.
The Recap
I highly recommend trying several different brands, sizes, and designs (jockey vs boxer cuts). If you start like this, instead of trying each of them one-by-one over 6+ months like I did, then you’ll quickly find a pair that you like and potentially become your preferred running shorts.
As for the ones that don’t work for you, simply send them back and enjoy the ones you keep.