Changing Destiny (Starfoil) (BP01-EN104) (BP01)

When an opponent's monster declares an attack: Target the attacking monster; negate the attack, and if you do, change it to Defense Position and it cannot change its battle position while it is face-up on the field. Then, your opponent chooses 1 of these effects:
• You gain Life Points equal to half the target's ATK.
• Your opponent takes damage equal to half the target's ATK.