When does a character's reaction reset, per turn or per round?

Question

When does a character's reaction reset, per turn or per round?

This happened last game and I'm just looking for clarification. My group has been playing (a 5e homebrew campaign) with an unspoken understanding that we each get one reaction per round. Last game, our fighter was next to last in initiative, and takes their turn without using a reaction. The top of the round starts and he wants to use his opportunity attack; no problems. Then, in the same round, he goes to use his reaction to use a homebrew item. He says his reaction resets per turn, not per round.

Can anyone clarify? Because both sides were pointing to the PHB.

Answer 1

Reactions reset at the start of your next turn.

Per the Player's Handbook, Chapter 9: Combat, on p190:

When you take a reaction, you can’t take another one until the start of your next turn.

So in your situation, if the fighter tried to use their reaction to interact with the homebrew item before the start of their next turn, they could not, since they have already expended their reaction taking an attack of opportunity.

Answer 2

It's not about the rounds

From the combat rules, on reactions:

When you take a reaction, you can't take another one until the start of your next turn.

This means that there are situations in which one could indeed have two reactions in the same round. Using your example, if the player took an opportunity attack before his turn came up, then at the start of his turn he can now do a reaction again, even if it is still the same round. However, he can't take another reaction until his turn comes up again (next round).

To illustrate how this works, here is a round by round breakdown. In this example the player is called Bob, fighting against enemies E1, E2, E3:

• Round 1
  • E1's turn (Bob's reaction is available)
  • E2's turn (Bob's reaction is available)
  • Bob's turn (Bob's reaction is available)
  • E3's turn (Bob's reaction is available)
• Round 2
  • E1's turn, Bob uses his reaction for an Opportunity attack
  • E2's turn (Bob can't take reactions at this point)
  • Bob's turn, he can now do a reaction again, including during his turn
  • E3's turn, Bob reacts using his homebrew item
• Round 3
  • E1's turn, (Bob can't take reactions at this point)
  • E2's turn, (Bob can't take reactions at this point)
  • Bob's turn, he can now do a reaction again, including during his turn
  • E3's turn (Bob's reaction is available)

(and so on...)

The main point is that rounds don't really matter for the purpose of reactions. Like the quote says, you can take 1 reaction, and you only get the ability to do so at the next start of your turn.

Answer 3

A reaction can be used once per round on anyone’s turn

A reaction is a once per round on any creature’s turn according to the PHB. Also remember that only certain spells and abilities allow you to use them as a reaction.

According to the rules on reactions (PHB, p. 190):

When you take a reaction, you can't take another one until the start of your next turn. If the reaction interrupts another creature's turn, that creature can continue its turn right after the reaction.