Joining a Grapple

If your target is already grappling someone else, you can use an attack to start a grapple, as above, except that the target doesn’t get an attack of opportunity against you, and your grab automatically succeeds. You still have to make a successful opposed grapple check to become part of the grapple.

If there are multiple opponents involved in the grapple, you pick one to make the opposed grapple check against.