Part 107 specifically mentions not flying over people that are not directly involved in the flying of your UAS, and I'm pretty sure the hobbyist guidelines have a similar guideline although I don't have access to those at the moment.
From the AMA Safety Code:
All pilots shall avoid flying directly over unprotected people, vessels, vehicles or structures and shall avoid endangerment of life and property of others.
You are required to follow such a safety code to fly as a hobbyist in the United States. If you don't, you are simply not authorized to fly at all.
And yes, I can cite chapter and verse, but I've done so in other threads.