This is my first post, so I hope I'm doing this correctly

It's game one in a best of three at a Competitive level event. Spells have been cast on each side of the table.

“Nolan” has 2 cards in hand and a single creature on the battlefield. There is a forest, a plains, and a mana confluence in play. “Alan” casts thoughtseize.

Nolan places his two cards face up on the table, a temple garden and a temple of plenty. Opponent writes down the cards, and ends the turn. Nolan draws for his turn, taps his still revealed temple garden, temple of plenty, and forest to cast unflinching courage. then realizes he hasn't picked up his two lands from last turn. The players call the judge.

What infraction has occured? Is it made worse that the played has tapped the lands for mana? whats the proper fix?

It's a Game Play Error (GPE), Game Rule Violation (GRV); I'd back up, put the two revealed lands back in his hand, untap the Forest, and put the Unflinching Courage back in hand - then have him carry one with his turn. Warning to Nolan.

You *could* assess a Failure to Maintain Game State to Alan, for allowing Nolan to leave his hand on the table through his untap and draw step - but that may not apply here. I've seen players leave their hand face up after a Thoughtseize, just to remind themselves which cards the opponent has seen.

d:^D

What's the actual rule being violated here? Tapping land that is sitting in your hand? (they're just revealed, we don't seem to be treating the situation as if he accidentally put them in play last turn)

Chris,

The actual GPV is for adding mana to his mana pool from a land in his hand. That is why Scott wants to backup to right before the casting of Unflinching Courage.

The part of his fix where he has the revealed lands back into the hand is not so much part of a rewind (they are technically there already as Alan never played them), but to help correlate the behavior that led to the error with the actual error; leaving them revealed to tapping them for mana.

Cheers,
-Bret