Does the Tank keyword apply when a spell triggers combat or only during physical combat between units?

Ruling: Tank only applies during actual combat between units contesting a battlefield, not when spells are involved. Spells don't trigger combat, and damage dealt by spells is never combat damage.

Nuances:

• Combat damage specifically refers to damage units deal each other during the combat damage step
• Damage dealt by units outside the combat damage step isn't combat damage
• Damage dealt by spells is never combat damage, even if dealt during combat