Poor communication causing a misunderstanding
Ruling issued on November 17th 2024

Situation:
An opponent is playing a mono-Terran arsenal. They have a resource tracker in front of them, showing they have 1 Terran resource remaining. Confident that the cheapest reaction to my card costs 2 Terran resources, I play a card. They then claim they forgot to update their resource tracking and react to my card using a Terran reaction costing 2 Terran resources. Are they allowed to use it?

Ruling:
The opponent should have communicated more clearly. In the spirit of fair play, it is their responsibility to provide accurate information about their board state. Even if they do have the required resources, their failure to update the resource tracking creates confusion at best and could be seen as deceitful at worst. Since this is their error, they are not allowed to play their reaction.