Can you break up your Attack action for a bonus action?

Question

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:

1. I have to wait until I finished all 4 attacks of the action, to make another attack as a bonus action
2. 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?

Answer 1

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).

You choose when to take a bonus action during your turn, unless the bonus action's timing is specified...

However, that tweet has been updated after realizing his mistake.

Clarification about bonus actions: if a feature says you can do X as a bonus action if you do Y, you must do Y before you can do X. For Shield Master, that means the bonus action must come after the Attack action. You decide when it happens afterward that turn.

He further clarified with this tweet

No general rule allows you to insert a bonus action between attacks in a single action. You can interrupt a multiple-attack action with a bonus action/reaction only if the trigger of the bonus action/reaction is an attack, rather than the action.

But that clarification was...wait for it...further clarified again:

"My tweet below was addressing bonus actions and reactions that have triggers. A bonus action that has no trigger—such as Cunning Action and the misty step spell—can take place whenever you want on your turn (PH, 189)

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.

Answer 2

So the answer here is #1:

I have to wait until I finished all 4 attacks of the action, to make another attack as a bonus action.

But I think it's important to really understand the wording here.

Wording from 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

Wording from Eldritch Knight - War Magic ability:

... when you use your action to cast a cantrip, you can make one weapon attack as a bonus action.

Notice the structure is the same here: when you ABC, you can XYZ as a bonus action. Remember, by default, you don't get a Bonus Action. You can only use Bonus Action if some trigger or ability gives you one. The wording above is effectively the trigger that gives you a Bonus Action.

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Frankly, as a player, this is really how you want it. If you crit on Attack #2, you want to finish the rest of your Attacks and then decide how you want to use your Bonus Action. There are lots of ways to trigger a Bonus Action and you only get to use one per turn, so this one may not be the correct one by the time you're done the Attack Action.

For example a Monk with Great Weapon Master may finish their Attack Action, trigger a Bonus Melee Weapon attack and realize that Flurry of Blows is a better use of their Bonus Action.

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In your particular example you get 5 attacks either way. The only weird exception is the fact that the 5th attack needs to be a "melee weapon attack". But ostensibly your first 4 attacks were already melee weapon attacks right?

Answer 3

I think the main point that is being missed is the first part of the sentence. Emphasis mine

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

So lets break this sentence up.

on your turn = when you can do the thing

when you score a critical hit = one possible trigger

when you bring something to 0 = a second possible trigger

you can make one melee weapon attack as a bonus action = the thing being done

On your turn means anytime until your turn is over after earning that bonus attack you can use it as long as you still have a bonus action to use. It doesn't say it has to be done immediately.

In the Player Handbook it says:

You choose when to take a bonus action during your turn

And while it doesn't specify you can, it doesn't say you can't choose to put that in between attacks from your attack action. And since you can already break up your attacks from the attack action with your movement:

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.

So, it kind of doesn't matter if you can or can't add them, because you functionally can't tell the difference between an attack action taken as part of your attack action, or as part of your bonus action from this, or any feature. because ingame AA attack, move, AA attack, BA attack is the same as AA attack, BA attack, move AA attack.

Answer 4

The answer is actually in your question. You gain a bonus action to attack one more time. You also get to move between attacks or strikes so long as you have movement. So in effect, you are just adding an attack to your attack sequence. It does not say you must take this bonus action immediately, it just says you get one for this turn.