The Legal Trap is one of the finest tricks you can play in chess: you give up your queen, the strongest piece on the board, and two moves later you deliver mate with a bishop and a knight. It’s named after Legal de Kermeur, an 18th-century French player said to have pulled it off in Paris around 1750. Nearly three centuries on, it still works against anyone who doesn’t see it coming.

The engine of the trap is a pin. And the idea to remember is that a pin isn’t always as solid as it looks.

The exact sequence

Here’s the classic line: 1.e4 e5 2.Nf3 d6 3.Bc4 Bg4 4.Nc3 g6?.

With 3…Bg4, Black pins the f3 knight against White’s queen on d1. That knight looks stuck: if it moves, the queen drops. So 4…g6? just keeps developing, no alarm bells. That’s exactly what White is about to exploit.

The g4 bishop pins the f3 knight to the queen — Black feels safe, but this is exactly where the sacrifice lands.

5.Nxe5!

The knight takes the e5 pawn as if the pin didn’t exist. Black, delighted, grabs the queen: 5…Bxd1??. And here comes the punishment:

6.Bxf7+ Ke7 7.Nd5#

The bishop takes f7 with check, the king is forced to go to e7 (it can’t take the bishop, defended by the e5 knight), and 7.Nd5 delivers mate. The black king is boxed in by its own pieces: the f7 bishop covers e6 and e8, the e5 knight covers d7, the d6 pawn blocks its own square, and Black’s queen and bishop occupy d8 and f8. No square, no defense. Mate with bishop and knight, White’s queen gone.

Mate with bishop and knight: the black king, stuck on e7, is smothered by its own pieces — and White's queen is long gone.

Why the pin doesn’t hold

It all rests on a calculation Black doesn’t make. Yes, taking e5 “loses” the queen. But in exchange, White gets a forced mate. A queen is worth nothing against a checkmate.

Black’s real move, after 5.Nxe5, is absolutely not to take the queen. It’s to recapture the knight: 5…dxe5. Then White plays 6.Qxg4 and wins back the bishop. The result? White has won a pawn cleanly, without any sorcery. Nothing dramatic for Black, just a pawn down.

There’s a detail that changes everything in this position, and it’s worth understanding. Here, Black played …d6 before …Bg4, without developing the knight to c6 to hold e5 a second time. As a result, after 5…dxe5 6.Qxg4, White’s queen isn’t threatened. If instead Black had a knight on c6 protecting e5, the sacrifice simply wouldn’t work: they’d recapture with the knight and win the queen for nothing. The Legal Trap needs f7 to be fragile and the queen to escape afterward.

How not to fall for it

One rule covers it: never grab a piece on reflex, and never the queen, without first checking what happens on the next move.

When you’ve pinned a knight to the queen and that knight moves anyway, treat it as a warning, not a free lunch. Your opponent has probably seen something you haven’t. Take three seconds to count the checks against your own king before you scoop up the queen. In the Legal Trap, all you needed to spot was the c4 bishop bearing down on f7 and the king with nowhere to run.

The other safeguard is development. If you hold the e5 square with a knight on c6 and castle quickly, this kind of swindle no longer has any grip on your position. Most opening traps punish a lack of development or a greedy capture, never a healthy position.

Learning it from both sides

You don’t remember a trap like this from reading about it. It sticks once you’ve set it yourself, felt the pin bite, then had to choose between grabbing the queen and calmly recapturing the knight.

Prologue lets you play both roles move by move: spring the trap as White and watch the mate land, then defend as Black and drill the one move that defuses it. For more patterns like this, see the traps and gambits guide.

Frequently asked questions

The mate only comes if Black takes the queen with 5…Bxd1. Against the right move 5…dxe5, White simply wins a pawn. The sacrifice only works because Black hasn’t defended e5 and f7 enough beforehand.

The Scholar’s Mate aims at f7 with the queen and bishop in the very first moves. The Legal Trap, on the other hand, deliberately sacrifices the queen to mate with bishop and knight. The first is a direct attack, the second a combination based on a pin.

After 6.Bxf7+, why can’t the king just take the bishop?

Because the bishop on f7 is defended by the knight on e5. The king on e8 can’t capture into a defended piece, so it’s shoved to e7, and 7.Nd5 finishes the job.

Where does the name of this trap come from?

It comes from Legal de Kermeur, an 18th-century French player and master of the Café de la Régence in Paris, credited with the first known execution of this mate, around 1750.