backdog

Defaming, insulting, or verbally abusing someone without their knowledge. This method of slander is often done behind the target's back, but can also be done in the person's presence without them being privy to the subject of the blaspheme. Regularly confused with 'backstabbing', backdogging someone is much more severe, with deep animosity and hostility almost always implied.

Tyler backdogged Grady, but Grady is so ignorant he had no idea what was going on.