The wording of the monk's Opportunist ability is confusing me slightly. It says :
Whenever a creature within 5 feet of you is hit by an attack made by a creature other than you, you can use your reaction to make a melee attack against that creature.
It uses a reaction, so it should only be possible once per round but it also says you can do it whenever the trigger occurs which suggests you can do it multiple times. Which is it?