Circle of Flame

Oracle Text

Whenever a creature without flying attacks you or a planeswalker you control, Circle of Flame deals 1 damage to that creature.

Card Rulings

7/18/2014 Circle of Flame’s ability triggers only if a creature without flying is declared as an attacker during the declare attackers step. If a creature with flying attacks you or a planeswalker you control and then loses flying, or if a creature without flying is put onto the battlefield attacking you or a planeswalker you control, the ability won’t trigger.