How do you move a creature encased in Otiluke's Resilient Sphere? Would an attack action like grapple-move or shove be legal? Can the creature inside even challenge the grapple or shove?
Or do you have to use the object lifting/pushing rules?
Lifting and Carrying
Your Strength score determines the amount of weight you can bear. The following terms define what you can lift or carry. Carrying Capacity.
Your carrying capacity is your Strength score multiplied by 15. This is the weight (in pounds) that you can carry, which is high enough that most characters don't usually have to worry about it.
Push, Drag, or Lift. You can push, drag, or lift a weight in pounds up to twice your carrying capacity (or 30 times your Strength score). While pushing or dragging weight in excess of your carrying capacity, your speed drops to 5 feet.
The problem with that is most monsters in 5e don't have listed weights and it doesn't account for the fact that pushing a sphere is easier than a block.
If there's no clear ruling I might home rule it so that a creature can push/pull an ORS of the same size or smaller but incur a 1/2 speed for every size larger.