Sentinel (pages 169–170, Player's Handbook) says
- Creatures within 5 feet of you provoke opportunity attacks from you even if they take the Disengage action before leaving your reach.
So one of my characters has the Sentinel feat and uses a glaive. The GM moved the bad guy back 5' so he's no longer standing within 5' of my character, then used the disengage action to avoid an OA, and then completed his original move action. Is this valid by RAW and/or RAI?
I know Rule 0 "the GM can rule however he wants".