When flipping Fight or Flight as a reaction, do you have to choose the target before your opponent can react, or after they react?

Ruling: You must declare targets for Fight or Flight when you finalize it (put it on the chain), before your opponent has a chance to react with other cards like Discipline.

Sequence:

• Finalize Fight or Flight by putting it on the chain and declaring your target
• Your opponent gets priority and can play reactions
• If no one plays anything else, Fight or Flight resolves and enacts its effect

Nuances:

• Finalize does not mean resolve - finalize is essentially the first step of playing a spell (similar to "on cast" in MTG)
• All cards with targets in Riftbound require target declaration as the card goes on the chain
• Some cards don't use targeting because both players make choices (like Cull the Weak)