Can you hide cards from your base, or only from your hand/champion zone?

Ruling: You can only hide cards from your hand or the Champion Zone, not from your base or battlefield.

Sequence:

• During your turn in an Open State, you may pay the hide cost for a card in your hand or Champion Zone
• Hide it facedown at a battlefield you control that doesn't already have a facedown card
• Beginning on the next turn, the hidden card gains Reaction and can be played, ignoring its base cost

Nuances:

• Cards in your hand or champion zone are neither ready nor exhausted (these states only apply to cards on the battlefield)
• If a unit like Teemo Scout is already at your base, you cannot hide it from there