Bashing Shield is a Equip 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, Bashing Shield is Unlimited.
YGOPRODeck lists Bashing Shield for these formats: Duel Links, Speed Duel, Common Charity, TCG, OCG, Master Duel.
A listed print of Bashing Shield appears in Battle Pack 3: Monster League (BP03-EN186) at Common rarity.
Among markets shown on this page, the lowest listed snapshot for Bashing Shield is about $0.21 on TCGPlayer (prices change frequently).
