Grappling And the Giant Scorpion
The PHB Pg.195 says when you want to grab a creature or wrestle with it, you can use the Attack action to make a special melee attack; a grapple. If you are able to make multiple attacks with the attack action, this attack replaces one of them. The target of your grapple must be no more than one size larger you and must be within reach.
The Giant Scorpion MM Pg.327 Claw Attack which it has two of, reach 5 ft. one target when hit is auto grappled (Specific case). Can you Make an Attack of Opportunity a Grapple attack? per standard Rules? and can the Giant Scorpion or another creature like get a opportunity grapple attack?