Once you have a reaction, you can’t have another one until your next turn. However, if your opponent takes his or her turn before you, you can have a reaction on your opponent’s turn. Then when your turn comes, you might be able to have a second reaction depending on what any one of your opponents does during your turn. Therefore, it is one reaction per turn, not per round. Every round has at least 2 turns: your side’s turns and the turn(s) of your opponent(s).