London System traps: 6 mistakes at 1200-1400 Elo

October 9, 2026 · 4 min read

At 1200-1400 the London is played on autopilot: d4, Bf4, e3, Nf3, Bd3, whatever Black does. Black has learned to fight the bishop on f4, and the games turn on loose pieces. A knight jumps to b4 without support, a bishop on f5 is left alone, or White plays the usual move one move too early.

We took the Lichess blitz and rapid games from August 2026 where both players were rated 1200 to 1400, followed the London move by move, and had Stockfish check every position where many players took the same wrong turn. Every line below was verified by the engine. All six examples are told from White’s side. For the main ideas of the opening, read our London System guide. One level down, see 6 mistakes at 1000-1200 Elo; one level up, 6 mistakes at 1400-1600 Elo.

Part 1: punish it

Three Black mistakes, three punishments. Each one leaves a piece without a defender, and the White queen or bishop collects it.

1. 6...Nb4, and the queen check

After 1.d4 Nf6 2.Bf4 Nc6 3.Nf3 d5 4.e3 Bf5 5.Bd3 Bxd3 6.Qxd3, 17% of Black players hit the queen with 6...Nb4. But the knight on b4 has no defender. 7.Qb5+! checks the king and attacks the knight at the same time. After 7...Nd7 8.Qxb4, White is a knight up. Most White players, 72%, found it.

Black should play 6...e6 instead, and the game is balanced.

6...Nb4? and 7.Qb5+! wins the knight.

2. 5...Ne4, and the d5 pawn falls

After 1.d4 Nf6 2.Bf4 Nc6 3.Nc3 d5 4.Nb5 e5 5.dxe5, 18% of Black players jump forward with 5...Ne4. The knight looks active, but it no longer guards d5. 6.Qxd5! takes the pawn, and 6...Qxd5 loses to 7.Nxc7+, forking the king and the queen. After 6...Bf5 7.Qxd8+ Rxd8 8.f3, White is two pawns up and winning. Only 17% of White players found 6.Qxd5; most played 6.e3.

Black should play 5...a6 instead and kick the knight first.

5...Ne4? and 6.Qxd5! wins material.

3. 4...Nf6, and the bishop on f5 hangs

After 1.d4 d5 2.Bf4 Bf5 3.e3 Nc6 4.Bd3, the two bishops face each other. 6% of Black players develop with 4...Nf6 as if nothing were attacked. 5.Bxf5 simply wins the bishop: nothing defends f5. White is a piece up.

Black should trade with 4...Bxd3 5.Qxd3 e6, and the game is balanced.

4...Nf6? and 5.Bxf5 wins a piece.

Part 2: avoid it

Now the White mistakes that come up most in the London at 1200-1400. In all three, White plays a normal-looking move and misses what Black is threatening.

4. 3.e3 against 2...h5

After 1.d4 d5 2.Bf4 h5, the pawn move looks strange, and 51% of White players answer with the automatic 3.e3. But 3...e5! hits the bishop. If 4.Bxe5 f6 5.Bg3 h4 6.Bf4 g5, the bishop is trapped. That is the point of 2...h5. Black wins a piece for a pawn or two.

Play 3.Nf3 instead. The knight guards e5, and White is a little better.

3.e3? and 3...e5! Play 3.Nf3 instead.

5. 4.Nb5 against 3...f6

After 1.d4 d5 2.Bf4 Nc6 3.Nc3 f6, 54% of White players jump to b5 to attack c7. But 4...e5! hits the bishop, and the knight has no follow-up. After 5.dxe5 fxe5 6.Bg3 a6 7.Nc3 d4 8.Nb1, the knight is back home and Black owns the center. Black is clearly better.

Play 4.Nf3 instead. Develop and keep an eye on e5, and the game is balanced.

4.Nb5? and 4...e5! Play 4.Nf3 instead.

6. 6.Qb3 when the knight can reach b4

After 1.d4 Nf6 2.Bf4 Nc6 3.Nf3 d5 4.e3 Bf5 5.c4 e6, 20% of White players attack b7 with 6.Qb3. But the queen has left d1, and nothing covers c2. 6...Nb4! threatens 7...Nc2+. After 7.Na3 c6, b7 is safe, the knight on a3 is offside and Black is better.

Play 6.Nc3 instead. The knight covers b5 and d5, and White is a little better.

6.Qb3? and 6...Nb4! Play 6.Nc3 instead.

What to take away

A knight that jumps to b4 without support can be hit by a queen check on b5 or a4.
When a black knight leaves f6, look at what it was guarding.
When the bishops face each other on d3 and f5, the one that does not trade may just hang.
Against an early ...h5 or ...f6, check what ...e5 does to the bishop on f4 before playing e3.

These patterns come from many games between players at your level, not from a theory book. Your own games have patterns too, and they are probably not the same ones. Chess X-Ray finds the moves where you lost your advantage in your chess.com or Lichess games, groups them by opening, and turns them into lessons you replay until they stick.