So I had an issue come up last night during one of our magic leagues, which I thought warranted a little better explanation. Since this was regular REL play, no blood was spilled; But since it seems like an interesting tactic, depending on the answer, I want to know how this works in a more competitive environment. Here's the scenario:

Adam and Nathan playing a game of standard. They are well into the game. Adam doesn't do anything during his post combat main phase, and says he's done. Nathan says: “Before the end of your turn ”Sphinx's Revelation for 7 (Nathan leaves 3 islands untapped) Adam says: "In response, cast Savage Summoning into Sire of Insanity. Go ahead and discard those cards.“

Nathan: ”No, Sire says at the BEGINNING of the end step, I was doing this DURING your end step“
Adam: ”No, you said before the end of my turn“
Nathan: ”I meant during your end step“
Adam: ”JUDGE!“

I came over, and after getting a feel for what happened, ruled that instants cast during the active players end of turn are assumed to be cast at the last possible moment before the turn changes, thus, DURING the end step. I also asked the opinion of another L1 who happened to be at the store, and his interpretation was a little different. After discussing it, we decided to go forward with my ruling.

In a competitive environment, how would this be handled, and how much does Nathans ”wording" actually contribute to the situation?

Edited George Bochenek (Nov. 7, 2013 02:48:54 PM)

Me: “Adam, what gives you the impression that Nathan would want to cast that before your end step?”

Adam should be very careful - i.e., honest - with his answer to that question. More than likely, he's grasping for an out, hoping the judge will support his (rather ludicrous) position. I'm not giving him that out - unless he convinces me that Nathan has, on every previous occasion, cast things during his second main phase instead of during his end of turn.

If Adam simply argues that “before the end of your turn” means “before your second main ends, and the Ending Phase begins”, then I'll explain that's not how it works; it's very rare that the opponent wants to act during the 2nd main, so it's usually (must be!) made very clear if that's the case.

Thanks - Scott Marshall