Hunted or Hunter (Red)

“When this defends” is an event-based trigger. Whether the attacking hero has played/activated a reaction is checked at the time Hunted or Hunter resolves on the stack and becomes a defending card (i..e defends the attack). If the trigger condition is met after this resolves, then this does not trigger.

If there is no attacking hero (e.g. this is defending against an ally attack), this does not trigger.