You can do it to move:
If you take an action that includes more than one weapon attack, you can break up your movement even further by moving between those attacks. For example, a fighter who can make two attacks with the Extra Attack feature and who has a speed of 25 feet could move 10 feet, make an attack, move 15 feet, and then attack again. (PHB 190)
It would be necessary for the Great Weapon Master feat:
On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action
As a level 17 Fighter, if I can not place a bonus action between attacks, there are two possibilities:
- I have to wait until I finished all 4 attacks of the action, to make another attack as a bonus action
- the bonus action attack is wasted unless the kill or crit happens on the 4th attack
So can I take a bonus action in the middle of the attacks of an action?
Best Answer
The language is unclear
The intent may have been that you must wait for your Action to complete before utilizing your Bonus Action.
Jeremy Crawford had previously tweeted that Bonus Action timing was completely up to the player regardless of the trigger requirement. While this gave a lot of freedom of choice, it wasn't really fully in tune with the written rules on Bonus Action timing (emphasis mine).
However, that tweet has been updated after realizing his mistake.
He further clarified with this tweet
But that clarification was...wait for it...further clarified again:
The RAW and the Crawford
It seems clear that Crawford's intent for Bonus Action triggers is that there is a requirement for the triggering Action to fully complete before you can take the Bonus Action. If you go by this, then you are not able to take your Bonus Action inside of (interrupting) your Attack Action.
A question of wording
However, as stated above, GWM is not triggered by the completion of an Action, but by the killing of or reducing an enemy to 0 HP. Given that the trigger is not based on the Attack Action but on the result of a hit combined with the rule on choosing when to take a bonus action during your turn, then it seems possible to interrupt your Action.
Which way to go?
I understand what Crawford is saying in that Actions are complete events that can not be interrupted...except by movement. His clarification that you can't interrupt one action (Attack) with another (Bonus Action) makes some sense, but given the precedent of allowing movement inside of an Action and that the trigger for GWM is not the Action but an event, a GM could rule at their table to allow it.
Crawford's intent here is understandable, but it still doesn't make 100% logical sense given that you can already interrupt your action with movement and/or reactions.
At my table, I generally let my players shift and shuffle actions as long as they aren't actually limited by a clear mechanic. In this case, it makes more than good sense to allow the player this and I haven't seen any issues with it at my tables.