Hey, I have a question. I'm defending a camp with a traveling merchant, enemy player attacks that camp with an overzealous fan. In his priority attacking player plays a spinning axe. Is it possible for defending player to answer to that spinning axe with a gust?

Yes, you can respond to the Spinning Axe with Gust.

According to the Showdown Timing Flowchart, once a Showdown has begun, the state is generally "Closed" when items are on the chain. During this time, players can alternate playing [Reaction] cards.

Here is the sequence of events based on your situation:

1. Initial Chain: The Overzealous Fan moves into the battlefield. Its "When I defend" trigger (if you were the one defending with it) or "When I attack" trigger (if it is the attacker) goes on the chain. (Note: Per your description, the Overzealous Fan is the attacker).
2. Attacker's Action: Once the initial chain resolves and the state becomes Open, the Attacker (with Focus) plays Spinning Axe. The state becomes "Closed."
3. Your Response: As the Defender, you have the opportunity to add a [Reaction] to the chain. Gust is a [Reaction] spell. You play Gust targeting the Overzealous Fan.

Why this works:

• Reaction Timing: [Reaction] spells can be played whenever a chain is "Closed" (meaning an item is already on the chain waiting to resolve) or when it is "Open."
• LIFO Resolution: Per Riftbound rules, the chain resolves Last-In, First-Out (LIFO). Because Gust was the last item added to the chain, it will resolve first, returning the Overzealous Fan to the hand before the Spinning Axe has a chance to attach to it (or resolve).

This interaction is consistent with the established timing rules for Riftbound, as seen in RiftJudge FAQ #9380 regarding the use of Gust in response to other chain items.