If an opponent moves his unit to a Reavers Row, and I have an Overzealous Fan on Row, can I order defender triggers and do Fan's ability before Reavers Row?

Yes, you can choose the order in which these triggers are placed on the chain.

According to RiftJudge FAQ #1695, when you control both Reaver's Row and Overzealous Fan and an opponent attacks into that battlefield, both abilities trigger as "When I defend" (or "When you defend here") triggers. As the controller of these triggers, you decide the order in which they are placed on the chain.

Sequence of Events:

1. Trigger Placement: The opponent moves their unit to the battlefield, initiating a showdown. Both Overzealous Fan and Reaver's Row trigger. You place them on the chain in your chosen order.
2. Chain State: The chain is now closed. Players may add reactions to the chain.
3. Resolution: The chain resolves in reverse order (Last-In, First-Out).
   • If you placed Overzealous Fan on the chain last, it will resolve first.
   • Upon resolution of Overzealous Fan, you may choose to kill it to move the attacking unit to its base.
   • Then, the Reaver's Row trigger resolves, allowing you to move a friendly unit to your base if you choose.

Important Nuances:

• Cost vs. Effect: As noted in RiftJudge FAQ #6503, killing Overzealous Fan is a cost paid at resolution. If you choose to use the ability, you must be able to kill the Fan (it must be on the battlefield) at that moment.
• Targeting: You must choose the target for the Overzealous Fan ability when you place the trigger on the chain, but the decision to pay the cost (kill the Fan) and execute the move is made during resolution.
• Trigger Conditions: Once a trigger is on the chain, it will resolve normally even if the trigger condition is no longer met (e.g., if the unit is no longer defending).

This interpretation is based on the mechanics of triggered abilities and the specific rulings provided in the Riftbound FAQ database.