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.