If my opponent plays a spell, I try to defy it, my opponent plays abandon to return defy to my hand, is it possible for me to allow abandon to resolve then counter the first card again?

Yes, it is possible for you to counter the original spell again after Abandon resolves.

According to the Chain Rules and Riftbound FAQ #9035, the chain is not a single, immutable block that must resolve all at once. Instead, it is a sequence of items that resolve one by one, and players receive a window of priority to add new reactions after each item resolves.

Sequence of Events:

1. Initial State: Your opponent plays a spell (let's call it Spell A).
2. Your Response: You play Defy targeting Spell A.
   • Chain (bottom to top): [Spell A] -> [Defy]
3. Opponent's Response: Your opponent plays Abandon targeting your Defy.
   • Chain (bottom to top): [Spell A] -> [Defy] -> [Abandon]
4. Resolution of Abandon: Abandon resolves first (LIFO - Last-In, First-Out). It returns your Defy to your hand.
   • Chain (bottom to top): [Spell A]
5. Priority Window: Because Spell A is still on the chain, the game enters a priority window before it resolves. Since you now have Defy back in your hand, you may play it again to target Spell A.
   • Chain (bottom to top): [Spell A] -> [Defy]
6. Final Resolution: Your new Defy resolves and counters Spell A.

This is possible because Defy is a [Reaction] spell, which allows you to play it from your hand whenever you have priority, including during the priority windows that open up while a chain is still resolving.