Backline

Backline is a Passive Ability keyword present on Units.

It is functionally short for "I must be assigned lethal damage after any other unit with the same controller as me that does not have [Backline] during the Combat Damage step."

It alters how players can elect to assign combat damage during combat. Players must still assign lethal damage to a unit before moving to the next when assigning their damage.

If more than one unit with Backline is present with the same controller in Combat, damage may be assigned to any of them. Units with Backline are invalid assignments until all units without Backline have lethal damage assigned to them.

Multiple instances of Backline are redundant.

Backline, and whether or not a unit has Backline, is a characteristic of the Unit and may be checked or referenced by other Game Effects.