Quote Originally Posted by HMS Invincible View Post
Q446 I grappled a prone creature. On the enemy's turn, he attacks me. Then on my next turn I cast sanctuary. On the creature's turn, it tries to break grapple. Do I lose sanctuary?
To clarify the question
1) Creature A successfully grapples Creature B who is prone
2) Creature B attacks Creature A
3) Creature A casts sanctuary (I presume targeting creature A)
4) Creature B tries to break the grapple and Creature A tries to maintain the Grapple.

Does Creature A lose the Sanctuary spell because it tries to maintain the Grapple with Creature B?

A 446 - No. Creature A is engaging in an opposed Ability Score contest and not attacking Creature B. This does not trigger the end of spell conditions for Sanctuary.

Note: If creature B escapes the grapple and Creature A tries to re-initiate a Grapple with Creature B then this would break the sanctuary spell as Grappling is begun by using the Attack Action and making a special melee attack. See pg 195 PHB under Grappling.