Legal's mate works only when moving the apparently pinned knight creates a forced mating threat and the defender chooses the poisoned queen. In the sound setup shown here, Nxe5! is a good move, but ...Bxd1?? is the losing choice. Black can decline the queen and capture the knight instead.
Use Back and Forward to replay the five half-moves from the critical position. Copy the current FEN at any step, then continue from the exact setup as White on the full Play Positions board. The practice opponent is free to choose a different defense.
Interactive lesson
Test the queen capture in Legal's mate
White to move: look beyond the pinned knight
The f3-knight appears tied to the queen on d1. White can move it because the bishop and both knights are ready to build a mating net around the uncastled king. The key question is what happens if Black takes the queen.
r2qkbnr/ppp2ppp/2np4/4p2b/2B1P3/2N2N1P/PPPP1PP1/R1BQK2R w KQkq - 1 6Play the critical position
Continue from the starting setup and calculate the game from the board in front of you. Choose a supported opponent and play to the natural result.
What is Legal's mate?
Legal's mate is an opening trap in which one side appears to leave the queen to a pinned bishop, then gives checkmate with a bishop and two knights if the queen is captured. The material count is a distraction. The real calculation is whether the king can survive the next two checks.
The pattern is named for the eighteenth-century French player Sire de Legal. Reports of the original Legal-Saint Brie game disagree about the date and move order, so this lesson does not claim to reproduce that score. It uses the commonly taught sound setup after 1.e4 e5 2.Nf3 Nc6 3.Bc4 d6 4.Nc3 Bg4 5.h3 Bh5.
Critical FEN: r2qkbnr/ppp2ppp/2np4/4p2b/2B1P3/2N2N1P/PPPP1PP1/R1BQK2R w KQkq - 1 6. Chess.js 1.4.0 replayed every lesson move. Stockfish 17.1 Lite, using one thread, 16 MB hash, full skill, MultiPV 3, and 3,000 ms, selected 6.Nxe5 and evaluated the position at +1.76 for White.
Why can the pinned knight move?
The knight on f3 is relatively pinned to the queen on d1, not absolutely pinned to the king. Moving it is legal. Usually that move would lose the queen, but chess does not end when a queen is captured. It ends at checkmate.
Before playing 6.Nxe5!, White has already prepared three minor pieces. The bishop on c4 points at f7. The f3-knight can capture e5 and then protects f7. The c3-knight can jump to d5. Together they can force the black king away from e8 and cover its escape squares.
The useful lesson is not "ignore pins." It is "compare the threat with the material loss." A relative pin can be broken only when the resulting checks, captures, or threats are concrete enough. Here the queen offer is justified by a verified mating line after the wrong defensive choice.
How the queen capture allows mate
After 6.Nxe5, Black has many legal moves. The tempting 6...Bxd1?? takes White's queen, but it does nothing for the exposed king. Stockfish reports mate in two for White from that position.
White continues with 7.Bxf7+. The bishop checks the king on e8, and the knight on e5 protects the bishop. Chess.js finds only 7...Ke7. Black cannot capture on f7 and cannot block the bishop's close-range check.
Now 8.Nd5# brings the other knight from c3. That knight checks e7. The knight on e5 controls c6, d7, f7, g6, g4, f3, d3, and c4; the bishop on f7 controls e8, e6, d5, c4, b3, a2, g8, g6, and h5. In the exact position, those pieces remove the king's legal escapes, while Black cannot capture the checking knight or interpose a piece.
The move order matters. White does not begin with Bxf7+ because the e5-knight must first protect f7. White also cannot finish with the knight already on e5; the c3-knight is the piece that reaches d5. The mate works because each minor piece has a different job.
How should Black avoid Legal's mate?
After 6.Nxe5, Black should first inspect White's checks instead of taking the most valuable visible piece. The queen on d1 can wait. Stockfish's best defensive choice is 6...Nxe5, removing the attacking knight. The sample principal variation begins 6...Nxe5 7.Qxh5 Nc4 8.Qb5+ c6 9.Qxc4, with White still better but no forced mate.
The exact evaluation depends on the position, so do not memorize ...Nxe5 as a universal answer. Use the decision process:
- List the checks: after taking the queen, what checks can the opponent give immediately?
- Follow forced replies: if a check leaves only one king move, continue that line before counting material.
- Remove an attacker: if declining the queen lets you capture the knight or trade a key bishop, compare that safer line.
- Count material last: a queen is valuable only if the game continues.
This is the defender's memory rule: checks before treasure. A hanging queen attracts attention, but the king's legal replies decide whether the capture is safe.
Common mistakes and the important exception
Playing Nxe5 before the bishop is displaced
In the earlier position with Black's bishop still on g4, Nxe5? may fail to ...Nxe5. The black knight removes the attacker and still protects the bishop on g4, so White does not even win that bishop with the queen. The move h3 and the bishop's retreat to h5 change the calculation.
Assuming the queen capture is forced
It is not. In the lesson position, Black has 36 legal replies after 6.Nxe5. The trap succeeds only if Black chooses ...Bxd1. An article board can demonstrate the punishment, but a live opponent may decline and continue a normal game.
Seeing the pattern without checking the squares
A bishop on c4 and knights on c3 and e5 are clues, not proof. Check whether the bishop's route to f7 is open, whether the e5-knight protects f7, whether the other knight can reach d5, and whether the king has an extra flight square. One changed pawn or developed piece can break the mate.
Calling every queen loss a sacrifice
A sound sacrifice has a verified return. If your forcing line ends before mate or adequate material recovery, leaving the queen en prise is simply a blunder. Calculate the opponent's best defense, not only the reply you hope to see.
Prepare, offer, check, close. Prepare the bishop and both knights, offer the queen only with a concrete threat, calculate every check after the capture, and close the net with the second knight.
Practise the critical position
Replay the lesson until you can name the job of each minor piece before pressing Forward. Then choose Defender Bot or Beginner Teacher. You play White from the exact starting FEN. Continue from the board in front of you and play to the natural result.
The read-only lesson verifies the queen-capture branch. The full Play Positions board is open practice with normal opponent and side controls. It does not promise 6...Bxd1, 7...Ke7, or any other demonstrated reply.
Use the piece-sacrifice guide to compare sound and speculative offers, and the tactics guide to train pins and forcing moves. The calculation guide helps you follow forced replies without jumping between branches. Compare this minor-piece net with the queen-and-knight geometry in the Smothered Mate lesson, then use the tactics trainer for mixed practice.
How this lesson was checked: Olivers Grants wrote the article, and developer and ML researcher Uldis Briedis reviewed the technical implementation. Chess.js 1.4.0 replayed every move and confirmed the final mate. Stockfish 17.1 Lite checked the starting position, the best decline, and the forced mate after the queen capture under the recorded limits. Public sources support the pattern and its historical uncertainty.