Can you use a reaction to an equipment being played or equipped?

Whether you can use a reaction depends on how the Equipment is entering play or being attached.

1. Attaching via an "Equip" Ability

Yes, you can react. According to RiftJudge FAQ #9560 and Rule 818.1, Equip is an activated ability. Activating it places the ability on the chain, which creates a Closed State and allows players to respond with [Reaction] cards or abilities before the equipment successfully attaches.

The Sequence:

1. Activation: The player activates the Equip ability on their gear, targeting a unit.
2. Chain Starts: The ability is placed on the chain.
3. Priority: State becomes Closed. Players may now play [Reaction] cards (e.g., removing the target unit).
4. Resolution: The chain resolves in LIFO (Last-In, First-Out) order. If you removed the target unit with your reaction, the Equip ability will fail to resolve.

2. Playing Equipment to the Battlefield

Generally, no. According to RiftJudge FAQ #5130 and #7617, when you simply play a piece of gear to the board (without using an Equip ability), it enters the chain and resolves immediately. Because it resolves instantly, there is no window for players to play a reaction.

Exception: If the Equipment has a "When I'm played" triggered ability (such as the Quick-Draw keyword, which triggers an attachment effect when played), that triggered ability does use the chain. You can react to that specific triggered ability.

This is my interpretation based on the referenced RiftJudge FAQs and Rule 818.1. No official ruling exists for every card interaction, but this is the standard behavior for the game's mechanics.