AoO question for 3.5: reach weapon on a diagonal!

Piratecat · Oct 9, 2017

My good friend is having a rules conflict, and I don't remember enough 3.5 to answer it:

D&D (3.5) question. Using squares where one diagonal square represents 5' and 2 diagonal squares represents 15':

Character A is two diagonal squares away from character B (an opponent).

Character B is wielding a reach weapon.

Character A casts a spell (not on the defensive).

Question: Does character A provoke an attack of opportunity?

Thanks for any advice! Bonus points for page references. The tricky question is the diagonals, and that pesky 5' / 10' difference.

AndromedaRPG · Oct 9, 2017

Yes, it is an exception to the diagonal rules. Page 137 of the Player's Handbook, fourth paragraph under “ATTACKS OF OPPORTUNITY.” The paragraph starts with “Reach Weapons.”

It can also be found here: http://www.d20srd.org/srd/combat/attacksOfOpportunity.htm#reachWeapons

Dannyalcatraz · Oct 9, 2017

The crucial language is:

Note: Small and Medium creatures wielding reach weapons threaten all squares 10 feet (2 squares) away, even diagonally. (This is an exception to the rule that 2 squares of diagonal distance is measured as 15 feet.

Greenfield · Oct 9, 2017

That's a good answer. So the follow up question would have to be, does it apply to creatures with 10 ft. reach as well? (It says that reach weapons are the "one exception".)

Dannyalcatraz · Oct 9, 2017

I would say that's an example of the rules writers not being lawyers and not recognizing the issue created by poor word choice, and apply the rule exception to natural reach as well.

After all, a 10' reach weapon gives you 10' of reach...which a creature with 10' reach already has.

Tony Vargas · Oct 9, 2017

Greenfield said:
That's a good answer. So the follow up question would have to be, does it apply to creatures with 10 ft. reach as well? (It says that reach weapons are the "one exception".)

The exception is necessitated by the 'doughnut' effect, for the AoO and threat rules to work with the adjacent dead-zone, the diagonal 'corners' have to be filled in, otherwise an enemy can walk through them, passing from 15' to 5' without ever passing within 10' - weird.

So it needn't apply to creatures with a natural 10' reach, though they should still get an AoO when an enemy moves from 15' to 5'... including (though it clearly does, RAW) spiked-chain wielders.

It's a fix - a kludge, really.
There was a similar flaw in the AoO rules with regard to conventional reach weapons: you could move through an ally's square, and cover prevented AoOs, and, while in an ally's square, you had cover. So one creature could move up to w/in 10' of the pole-arm user, and then up to 8 of his allies could walk through his square, and around the guy with the polearm, to completely surround him. Don't recall if that one was ever kludged.

Greenfield · Oct 12, 2017

The problem I see is that feats like Large and In Charge, which flat stop someone from approaching don't work on someone approaching on the diagonal.

The AoO is triggered when an opponent *leaves* a threatened square, and takes place while they are still in it. If there isn't an actual "threatened square", then feats and maneuvers designed to stop them from leaving that square, such as Large and In Charge or Improved Trip become meaningless. The opponent still gets to move into striking distance.

Additionally, consider what happens in the other direction: You're toe to toe with a Giant and your PC is about to fall. Withdrawal gives you the first five feet of your "Run like Hell" move without AoO. Normally that isn't enough against a foe with Reach, if you start out in an adjacent square. If you can slip that by fleeing on a diagonal, however, that hole in their threatened zone is a hole in the rules.

So I'm thinking that the same two-square rule should apply to creatures with reach.

YMMV, of course.

Tony Vargas · Oct 13, 2017

Greenfield said:
So I'm thinking that the same two-square rule should apply to creatures with reach.

Sounds reasonable - but most of 'em are large creatures with 10' areas to start, so their threatened area isn't the same shape as a medium creature with a reach weapon. Counting diagonal distance is just slightly problematic in 3.x - if it were 5e, we'd just say 'trust your DM to make a reasonable ruling' (or you're the DM, make a reasonable ruling)....

You might want to rule that square threatened for some purposes, not others. It is, in effect, two squares, a creature in it is both 10 and 15' away from the guy with 10' reach. You could even place the figure on the intersection at the far corner of the problematic square to indicate it being 15' away, and in the square, itself, for 10', if you wanted to be more exact (and also cover the case of insufficient diagonal movement to enter a square).

Greenfield · Oct 13, 2017

Let's consider a Large creature X.

O O O O O O
O O O O O O
O O X X O O
O O X X O O
O O O O O O
O O O O O O

Look at the diagonals. His 10 foot reach is two squares, whether he occupies 1 square, four squares or nine squares.

So an opponent standing at one of those corners, and Withdraws on that diagonal course, he would draw no AoO. Withdrawing on any other course would draw the AoO when leaving the second square.

That's the hole I was referring to, and it doesn't disappear when you scale it up or scale it down.

And that's why I think that ten foot Reach has to go two squares, at any angle, whether it's a Reach weapon or a natural weapon.