The vampire spawn's claw attack reads:
Instead of dealing damage, the vampire can grapple the target (escape DC 13)
When exactly is this decision made? In particular, I am interested in the interaction with the Drunken Master's Redirect Attack:
When a creature misses you with a melee attack roll, you can spend 1 ki point as a reaction to cause that attack to hit one creature of your choice, other than the attacker, that you can see within 5 feet of you.
Can the vampire spawn choose to simply grapple to avoid hurting an ally after the attack has been redirected?