Source: Player's Handbook

Prerequisite: Strength 13 or higher

You've developed the skills necessary to hold your own in close-quarters grappling. You gain the following benefits:

• You have advantage on attack rolls against a creature you are grappling.

• You can use your action to try to pin a creature grappled by you. To do so, make another grapple check. If you succeed, you and the creature are both restrained until the grapple ends.