How many Opportunity Attacks (OA) does a PC get per round?
Example: if multiple foes go by a PC engaged in combat, and leaves their weapon reach, does the PC get an OA against each creature that goes by it?
Moving Around Other Creatures
If you leave a hostile creature’s reach during your move, you provoke an opportunity attack ...(Basic Rules p. 71:)
You can make an opportunity attack when a hostile creature that you can see moves out of your reach. (Basic Rules p. 73)