If we start a chain of reactions and triggers as we resolve them, can other reactions be played into the chain such as Discipline being resolved mid-chain to draw Defy and then playing Defy before the first spell is resolved?

Yes, you can absolutely do this. In Riftbound, chains do not resolve all at once; instead, they resolve one item at a time, and players have opportunities to add new reactions to the chain between each resolution.

How it works:

1. Chain Resolution: When a chain is resolving, the top item resolves first.
2. Priority Window: After an item resolves, the chain is not yet empty. Before the next item on the chain resolves, both players are given a new opportunity to play reactions.
3. Playing New Cards: If a card effect (like Discipline) causes you to draw a card (like Defy) mid-resolution, you are free to play that newly drawn card as a reaction to the remaining items on the chain once you receive priority.

The Sequence:

• Chain is built: Multiple items (including Discipline) are on the chain.
• Resolution: The top item resolves.
• Priority: After that item resolves, priority is passed. If you draw a card from that resolution, you can now play it as a reaction to the next item on the chain.
• Adding to the Chain: You add your new reaction (e.g., Defy) to the top of the chain.
• New Resolution: The chain now resolves your new reaction first, before moving on to the previous items.

According to RiftJudge FAQ #7449: "Players can play reactions during chain resolution, not just before it starts. After each chain item resolves, if more items remain on the chain, priority goes to the controller of the next chain item, and both players can add new reactions before the next item resolves."

This process repeats until the chain is empty. You do not have to wait for the entire chain to finish resolving to play a card you just drew.