740. Shield

740.1. Shield is a Passive Ability keyword.

740.1.a. It is present on Units.
740.1.b. Shield is formatted as "Shield [X]".
740.1.b.1. The X is referenced in the functional text of the ability.
740.1.b.2. The X is referred to as the Shield Value.
740.1.b.3. If X is omitted, it is presumed to be 1.
740.1.c. It is functionally short for "While I am a defender, I have +X [M]."
740.1.d. Being a defender means the Unit has gained the Defender designation during Combat. See rule 437. Combat for more information.
740.1.d.1. Shield remains in effect as long as the Unit maintains the Defender designation.

740.2. If a Unit has Shield, or has been granted Shield, and is granted Shield by an additional source, the Shield Value of all granted Shield keywords is summed. Example: Stalwart Poro has Shield. It is chosen as the target of Block, which says "Give a unit [Shield 3] and [Tank] this turn." After Block resolves, Stalwart Poro has Shield 4 this turn.

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