I am running a barbarian and fighter multiclass. When raging, I have resistance to all bludgeoning, piercing, and slashing damage. And the fighter Battle Master Maneuver Parry allows me to expend a superiority die to reduce damage. It is unclear in which order these would trigger. Rage halve it then Battle Master die lower it? Or Battle Master die then rage halve it? (I don't think this is stacking resistance since the Parry isn't resistance.)
Parry reduces the damage, then Resistance halves the remainder.
Per DnD Beyond, Wizards of the Coast's official rules resource, "Resistance and then vulnerability are applied after all other modifiers to damage." So you Parry the hit to deflect part of the damage, then whatever's left gets through, hits you, and gets halved by your resistance.