Can you Grapple a Creature that has already Grappled you?

Question

Suppose an ettercap sneaks up on Bob the Barbarian whom is trailing his group and attacks him with a web garrote, inflicting Bob with the Grappled condition. Normally this is to the ettercap's advantage, but Bob is fine with grappling and feels the scenario is closer to the ettercap being trapped with him.

In order to ensure that this sneaky enemy can't escape, Bob wants to turn around and grapple the ettercap, to force it to hold still while Bob's allies rain pain on it from afar.

Can Bob do this without breaking the original grapple? If so, are both creatures considered to have the Grappled condition and thus have a speed of 0?

Answer 1

Yes, you can try to grapple an enemy who is grappling you.

The rules for grappling are...

The target of your grapple must be no more than one size larger than you, and it must be within your reach. Using at least one free hand, you try to seize the target by making a Strength (Athletics) check[...]

PHB195

The effect of a Grapple is...

• A grappled creature's speed becomes 0, and it can't benefit from any bonus to its speed
• [Rules on how to get out]

PHB290

There's nothing in here that prevents you from counter-grappling, as long as you have a free hand and can reach your target. In which case you are both subjected to the Grappled condition, and now neither one of you can move without breaking the grapple first.

Answer 2

Yes, you can grapple a creature who has grappled you.

From the PHB pg. 290:

Grappled

• A grappled creature’s speed becomes 0, and it can't benefit from any bonus to its speed.
• The condition ends if the grappler is incapacitated (see the condition).
• The condition also ends if an effect removes the grappled creature from the reach of the grappler or grappling effect, such as when a creature is hurled away by the thunderwave spell.

None of the effects imposed by being grappled prevent you from attacking or grappling a creature in return. And when you do grapple the creature, it also suffers the effects of the grappled condition.

If it helps, try picturing two wrestlers (actual wrestlers) who are cinched trying to move the other one. Both of them are immobilized until one manages to break the other's hold and go for a pin.