It’s Time to Drain the _________

You are the Head Judge of your local Standard PPTQ. You have collected all the decklists and round 1 has begun. While ensuring that all of the lists are present, you notice that one player has a blank line with a number next to it on his decklist. He is playing Black/White control, and has registered

(42 other cards)
4 Concealed Courtyard
6 Plains

What do you do? Consider when you would like to talk to the player, what you’re going to tell them, and what infractions and/or penalties they will receive.

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As the Head Judge, you have the option to not apply Decklist Problem here. The player has submitted what appears to be an illegal decklist, but it is obvious that the card in the blank is Swamp. Double check that the player is indeed playing Swamps, and after the round find them and let them know that you fixed the list and to be more careful in the future.