Ring of Defense is a Quick-Play Spell Card.
Spell Cards are usually activated from the hand on your turn unless their type gives another timing window.
On the current TCG and OCG Forbidden & Limited lists tracked here, Ring of Defense is Unlimited.
YGOPRODeck lists Ring of Defense for these formats: Duel Links, Common Charity, Edison, TCG, OCG, Master Duel.
A listed print of Ring of Defense appears in Duelist Pack: Chazz Princeton (DP2-EN026) at Ultra Rare rarity.
Among markets shown on this page, the lowest listed snapshot for Ring of Defense is about $0.13 on TCGPlayer (prices change frequently).
