I get from the PHB that there is no general rule for disarming an opponent but only a specific rule for Battle Master fighters.
Can we assume that other classes (even other fighters subclasses) lack the training for such move or can we deduce that everyone can attempt a disarm without the superiority dice?
Best Answer
The closest thing to a general rule I can see is the sidebar in the section on Grappling/Shoving a Creature (Basic Rules p.74):
It certainly seems like the intention of a section like this would be to allow you to attempt special maneuvers (such as disarming) as an action in combat via a contest if you're not as trained as the Battlemaster, but, as always, it's up to the DM.
As of the DMG's release (DMG p.271), there is an officially suggested contest for disarm attempts (though, to be clear, it is still an optional rule/action that may or may not be present in any given DM's game):