In a Modern GPT you are head judging, Andrew has a Kataki, War’s Wage, a Birthing Pod, and a Wall of Roots in play. He begins his turn by untapping and drawing for his turn. In his Main Phase, Andrew activates Birthing Pod by tapping two lands and sacrificing Wall of Roots. He begins searching his library. Before he has pulled a card out, his opponent Nathan stops him and says, “You forgot to pay for Kataki on your Birthing Pod.” Both players call for a judge. What do you do?

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[expand title=Answer]The trigger that Kataki grants to Birthing Pod is a detrimental trigger as well as being a trigger that has a default action. Andrew will receive a Warning for Missed Trigger. Since it has a default action, we will give the opponent the choice of when to resolve it; the next time a player would receive priority or the first time a player would receive priority in the next phase. Either way, Andrew will finish resolving Birthing Pod as it has already been activated and is currently being resolved. It’s very tempting to try to back-up the game to before the Birthing Pod activation because it “feels right” or “it’s not fair that he still gets the Birthing Pod activation.” While Nathan isn’t required to point out Andrew’s triggers, it’s still in his hands to point out Andrew’s triggers that he wants to happen when they are supposed to happen. However, Game Rule Violation and Communication Policy Violation are the only infractions that would allow us to back-up the game and neither of those infractions have been committed. The infraction committed is Missed Trigger and the remedy for Missed Trigger does not allow for a back-up of the game state.[/expand]