Bastion

The Warforged is hiding as good as he can by standing not far away from the door, leaned from the inside on the wall, so he would only be seen once someone entering the door turns around. Standing still, he waits whether action on his side proves to be required.

Should the guard decide fleeing to be a good option, Bastion would step into the door and try to tackle the man to the floor.

Spoiler: OOC
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I understand the situation as defused for the moment, but in case it is required, here's an Strength (Athletics) roll which can be the resisted by Athletics or Acrobatics.
(1d20+11)[17]