Reach on and off weapons

[elyktsorb]

So the Reach weapon property states that it effects your opportunity attack area of influence.

Does this mean that things that increase your reach, but do not have the reach property, don't effect your opportunity attack area of influence?

[JackPhoenix]

Opportunity attacks happen when the enemy leaves your reach (and in few other circumstances with certain abilities). It has nothing to do with Reach weapon property.

[Lalliman]

To further clarify, the rules for opportunity attacks state: "You can make an opportunity attack when a hostile creature that you can see moves out of your reach." So anything that increases your reach affects opportunity attacks. A giant ape, for example, has its opportunity attack threshold at 10 feet, matching the reach of its attacks.

The reason why reach weapons specifically point out opportunity attacks is probably mostly for clarity, or else new players might not realise this fairly important aspect of reach weapons. There is however a niche difference between having 10 foot reach naturally and having it from a reach weapon. The reach weapon increases your reach for the purpose of attacks and opportunity attacks, but not for other purposes, such as freeing another creature from a net.

The rules for the net state: "A creature can use its action to make a DC 10 Strength check, freeing itself or another creature within its reach on a success." So a giant ape can free a creature 10 feet away from a net, but a humanoid with a reach weapon can't, because the weapon increases their reach only for the purpose of attacks and opportunity attacks, which this isn't. There are probably other actions where this distinction applies, though I can't think of any.

As an aside, it is possible to have reach that doesn't affect opportunity attacks. Bugbears have 10 foot reach only for the purpose of attacks during their turn, so their reach for the purpose of opportunity attacks is still 5 feet. But again, that's niche.