After twenty moves, the OTB game likesforests vs careyfan arrived at this position:

(1) What should White play?

(2) White actually played 21.Na4. What should Black play?

White to play Nxe4?

With Na4, I was thinking of

1... Bxg2

2. Kxg2 Qxe3 Black wins pawn

3. f2xe3 Nxe3 Black gets a fork with King/Queen/Rook

But I don't think that could be right, but looks like Black wins a pawn if they didn't take the queen.

Gonnosuke> 1. White can remove the guard on the c4 knight, pick up a pawn and put a nice dent in blacks pawn structure with Nxe4 Bxe4 Bxe4 dxe4 Qxc4.

Bingo!

Gonnosuke> If there's a tactical shot after Na4, I don't see it.

I didn't either. Careyfan found a nice one! 1.Na4? Bxg2! 2.Kxg2 Qxe3! and 3.fxe3 is met by 3...Nxe3+, so in the actual game I played 3.Qc3 Qf3 4.Qxf3 Rxf3 instead but now the a3 pawn also falls and Black had a huge lead. Note, 3.Qxc4?? fails due to 3...Qf3+.

LearnChess> But I don't think that could be right

You're exactly right. :)

A forking motive! Nice!

But I have a question: What will happen after

1. Nxe4 Qg6

I do not see,that white can get out of that pin! But perhaps I have not searched deeply and long enough !?

Nice tactic.  Even when it's flagged up as a puzzle, the fork isn't easy to spot at all.  Not by me anyway!

mauerblume> [21]. Nxe4 Qg6!

Wow, this position is full of surprises... good spotting.

Gonnosuke> 22.Bxf3 23.Rac1 Nxa3 24.Qa2 +/-

I played out your lines and double-checked with Rybka this time--they're correct!

Hey likesforests.  It was a pleasure meeting you at the tourney, and thanks for posting this puzzle.

I overlooked Nxe4 during our game.  Not sure how I would've responded to that...although Qg6 (as someone mentioned) looks interesting.  Still, it definitely would've complicated the game for me. 

It was an interesting game.  I think tactics trainer on chess.com is helping me a little bit, as it has a lot of forking motif puzzles.