How many creatures can attack (melee) a single creature at once (assuming all creatures are medium sized)?

Question

Regarding a hypothetical scenario where you have a party of 8 PC's and one enemy. Can all of those 8 PC's surround and attack the enemy creature (following a square 5x5 feet square grid) in one round?

Another hypothetical scenario where an army of 1000 (all wielding swords) exists. How many members of the army can attack a single creature at once?

Answer 1

If the target is Medium sized and the PC's are medium sized, they can surround and attack it. From the PHB pg 191:

Assuming Medium combatants, eight creatures can fit in a 5-foot radius around another one

Further down on page 192:

In contrast, as many as twenty Medium creatures can surround a Gargantuan one.

This, however is not accounting the fact that creatures can, in the same turn, move closer, attack and retreat (possibly provoking an opportunity attack), leaving room for another to attack in the same round. If you factor that in, depending on the attacker's speed you can fit in far more creatures attacking in the same round.

Answer 2

Can all of those 8 PC's surround and attack the enemy creature (following a square 5x5 feet square grid) in one round?

Yes, trivially answered on PHB p.191.

How many members of the [thousand-person] army can attack a single creature at once?

All of them.

Assuming two dimensions, swords, and no movement, you'll get 24 medium attackers.

8 medium creatures with 5' reach surround the medium target.

16 medium creatures with 10' reach surround the medium target. Per your question they can only have swords, but you can also give them the lunging attack maneuver.

That's not much, though. Only one-fortieth of your army...

With movement you can easily get 840 medium attackers.

With movement you're limited to the number of characters that can get to within 10' of the target, pull off a lunging attack, and get back to their starting position. Actually, there's lots more, but these are the ones that are easy to think about.

Obviously it's nice to have a lot of movement, so let's go with Tabaxi monk 18/fighter 2 using its feline agility: 30' (Tabaxi) + 30' (unarmored movement) is 60' walking speed. Feline agility doubles this to 120'. Step of the Wind allows this attacker to Dash in addition to attacking, so that's 240' of movement available. Assume it's all through difficult terrain--other attackers--so movement costs double.

r=1 (squares): 8 attackers, no movement, shortsword attacks.

r=2: 16 attackers, no movement, lunging shortsword attacks.

r=3: 24 attackers, 5' movement each way (costing a total of 20'), lunging shortsword attack.

r=4: 32 attackers, 10' movement each way (costing a total of 40'), lunging shortsword attack.

r=5: 40 attackers, 15' movement each way (costing a total of 60'), lunging shortsword attack.

[...]

r=14: 112 attackers, 60' movement each way (costing a total of 240'), lunging shortsword attack.

That's a total of 840 attackers.¹

But wait, there's more!

That wasn't actually a very efficient use of attackers' motion. You'll note that most ended the round with some movement unused, and some didn't even use any! Let's fix that.

Starting from the inside, let us suppose that the 8 attackers at r=1 used all their movement to go 120' away after attacking. This means that eight attackers from 120' away could come in and take their places. Likewise the 16 attackers at r=2 could use all their movement to go 125' away; 16 attackers from 125' away can swoop in and take those places. The 24 r=3 attackers move 5' in and 5' back as before, then move 110' out; 24 more attackers at 110' range can move all the way in to lunge-attack and end at r=3.

In this manner we can pretty-quickly double the number of attackers who can reach the target, far exceeding your 1000-creature army. (Actually, it's not quite doubling, since our r=14 ring of attackers don't have "buddies.") This works out to 1568 attackers.²

But wait, there's a lot more!

Note that all of the above assumed that all of each attacker's movement was through difficult terrain. But that need not be the case: we could sequence the movement of attackers so as to leave much movement unhampered. Imagine in the scenario above if the innermost four rings of attackers attack first, then clear out to the extent of their movement. Now, when later rings attack their last 10' in and first 10' out are not difficult terrain. This means that r=14 attackers returning to their starting position have 20' unused movement.³ And that r=15 attackers can make it in-and-back! By clearing out r=1-4 first we've made it possible for r=15 to be the outermost ring. Likewise clearing out r=5-8 next will make r=16 the outer limit, clearing r=9-12 pushes the limit to r=17, clearing r=13-16 makes r=18 the outer limit. And we've pushed the number to 2592 attackers.⁴

But wait, there's a LOT more!

Consider: we haven't even touched various other speed-enhancers. Haste, various Boots of ..., mixing monk and barbarian unarmored movement, &c. See what's the fastest a character can move in one turn? for a primer on why the true answer to this question might be in the millions. All attacking from the horizontal plane.

And then there's the hypothetical third dimension. If our attackers can have burrowing or flying speeds we can extend the above arguments in many directions. Just the two horizontal planes 5' above and below the target will serve to triple the number of attackers (Assuming you can manage base movement while flying/burrowing.) Off the top of my head, fully-utilizing three dimensions is going to roughly square the number of attackers in range!

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^{1 - The attackers within a range \$r\$ of the target cover a square \$2r+1\$ on a side. Thus the number of attackers within \$r\$ of the target equals \$(2r+1)^2 - 1\$ (the target).}

^{2 - We sum up the attackers within \$r=13\$, double that, and add in the \$r=14\$ ring: $$2\times [(2\cdot13+1)^2-1] + (8\cdot14)=1568$$}

^{3 - Obviously, then, the r=14 ring will not return to r=14, but rather to r=16. And another 112 attackers from r=16 can come in, attack, and end up at r=14. This reasoning continues until we find the "true" outermost ring.}

^{4 - as in note 2.}

Answer 3

All of them/arbitrarily large:

(With thanks to @Joel Harmon for the idea, and his blessing in posting it.)

Let your army consist of battlemasters (fighters) of at least level 17. Let us assume your target is not proficient in STR saves, and has a STR mod of 0.

Line your battlemasters up in two lines, separated by 10', and have every one of them drink a potion of fire giant strength. Lastly, every battlemaster but the one at the end of one line, next to the target, should Ready a pushing attack for when the target comes in range. The starting setup looks like this, where numbered entries are battlemasters and a represents the starting position of the target.

1  3  5  7  9  11 13 15 ...
   a

2  4  6  8  10 12 14 16 ...

the attack begins:

Battlemaster 1 executes a pushing attack. The DC for the target's STR save is 8 + 6 (prof) + 7 (pot. of fire giant str.) = 21, which cannot be achieved by our target with +0 STR save.

and continues...

1  3  5  7  9  11 13 15 ...
   a     c     e     g
      b     d     f
2  4  6  8  10 12 14 16 ...

• 1's attack pushes target to position b
• 3 chooses to make an OA, spending its reaction and nullifying its Readied attack
• 4 executes its Readied pushing attack, pushing target to position c
• 6 chooses to make an OA, spending its reaction and nullifying its Readied attack
• 5 executes its Readied pushing attack, pushing target to position d
• 7 chooses to make an OA...
• 8 executes its Readied pushing attack...
• 10 chooses...
• 9 executes...
• 11 chooses...
• 12 executes...
• 14 chooses...
• &c. &c. &c.
• 2 says "awww..." and hastily assembles a peasant railgun to ride and thereby catch up to the target.

Answer 4

120 stationary melee attackers on the ground, including a mix of Fighters, Bugbears, and Monks

This answer hinges upon the reach outline here: What build maximizes reach?

That allows us to have a total of five "layers"; the calculation of the resultant square being pretty straight forward of: \$(\text{layers} \times 2 + 1)^2 - 1\$.

$$(5\times 2 + 1)^2 -1 = (11)^2 - 1 = 120$$

Without any shenanigans from movement, any flying, or readied actions, 120 people (at least 40 of which are bugbears) can attack a single target that they are centered/grouped around.

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• The first "layer" (8) can be any melee combatant to reach the 5 feet.
• The second "layer" (16) must either be Battle Masters, Bugbears, or Elemental Monks to reach the 10 feet.
• The third "layer" (24) must be Elemental Monks or Bugbear Battle Masters to reach the 15 feet.
• The fourth "layer" (32) must be Elemental Monks and one either a Battle Master or a Bugbear to reach 20 feet.
• The fifth and final "layer" (40) must be Multiclass Bugbear Battle Master Elemental Monks to reach 25 feet.