Isn't that Petroff's Defense?
And are you talking about a trap for white or a trap for black? Since both sides can be trapped if played wrongly.
Deadliest Opening Traps


Any trap, really. And yes, that's usually called the Petroff Defense, but it also goes by the Russian Game.

Any trap, really. And yes, that's usually called the Petroff Defense, but it also goes by the Russian Game.
Yes, but I meant in YOUR game. I couldn't figure which side was the trap laid for exactly there.

Anyone remember how the one trap in the Ruy Lopez goes where the white bishop runs out of squares and gets trapped by black's pawns on the queenside? I've done that one in games before but not for a couple years. I don't remember but I think it may be out of the Berlin.
One trap that works surprisingly often is the QGA trap where black tries to keep his pawn and white plays Qf3 attacking the rook on a8. Only way to defend properly is for black to give up the knight.

Oh, didn't see that when I posted. True, that would have definitely won him the game. But hey, give me some slack, because when I first played this I didn't know about Legal's Mate at all. I just suddenly saw a possible mate in two, and played what I thought was the best move. My opponent in that game is probably the best player in my immediate acquaintance, and that's still one of only three games I've won against him (he told me that that was called a Legal's Mate). Nxe5 would have won, but most people, even my opponent who obviously knew about it, would probably think it a mistake and take the queen. Very effective trap, albeit a bit risky.
I'm sure most have seen this infamous trap hidden in the Russian Game:
I've popped the trap a few times myself. Does anyone else have a Deadliest Opening Trap?