The Under Armour Project Rock 5s have received mixed reviews from users when it comes to whether they run small and whether they fit true to size.
I can only speak on my own personal experience, and I would say that they do in fact run true to size.
It's very important to remember that fit varies from person to person, we all have different foot shapes and preferences, but do make sure you measure your feet and compare it to the size chart over on the UA website especially if you haven't owned UA shoes before.
Also, it is never a bad idea to try the shoes on in-store or order them online with a free return policy if possible to ensure you get the best fit possible.