Can I move a unit to a battleground controlled by a friendly player in 2v2 if they aren't in combat?

Ruling: You cannot have one of your units on the same battlefield as one of your teammate's units, ever.

Nuances:

• If an enemy moves to a battleground controlled by your teammate, it results in a normal showdown
• You can move your teammate's units to a battlefield that only has an enemy unit on it, since your teammate's units are friendly