Under the "Grappled" condition in the compendium, it leaves out that grappled creatures have disadvantage on Dexterity saving throws.

This is the SRD rules for grappling:

• 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.