Chess Openings Lab
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Sicilian Defense: Smith-Morra Gambit Accepted, Paulsen Formation

The Paulsen Formation of the Smith-Morra is 4...Nc6 5.Nf3 e6 6.Bc4 a6, where Black covers b5 and prepares ...b5 to gain time on the c4 bishop. White wants to castle, develop with Bf4 or Qe2, and play e5 before Black's queenside expansion arrives.

Moves
1.e4 c5 2.d4 cxd4 3.c3 dxc3 4.Nxc3 Nc6 5.Nf3 e6 6.Bc4 a6
ECO
B21
Engine
−0.34 · a slight edge for Black (Stockfish 17.1, depth 20)
Played
805 games in our lichess sample
White scores
51.9%

Key ideas for both sides

White

  • Castle with 7.O-O and meet ...b5 with Bd3, keeping the bishop aimed at Black's kingside.
  • Bf4 and Rc1 put pressure on the c-file and the d6 square while Black's kingside is undeveloped.
  • Qe2 and a later e5 gain space and make it hard for Black to play ...Nf6.

Black

  • Play ...b5 and ...Bb7 to hit e4 and gain a tempo on the bishop.
  • Develop with ...Nge7 and ...Ng6, as in the Bf4 line, to challenge White's dark-squared bishop.
  • Use ...Bd6 and ...Bc7 to cover e5 against White's push and keep the bishop near the king.

Plans and pawn structure

Black's queenside pawns roll first: ...b5 kicks the c4 bishop to d3, and ...Bb7 points at e4. White's compensation is development and the open c- and d-files, so White plays Bf4, Rc1 and Qe2, looking for e5 or a knight landing on d5. Black's king usually castles late after ...Nge7 and ...Ng6. The side that finishes development first sets the tone.

Where the engine's main line heads: Open Sicilian: White traded the d-pawn for Black's c-pawn. An Open Sicilian: White traded the d-pawn for Black's c-pawn. White has a lead in development and the d-file, Black has the half-open c-file and two central pawns.

What the engine plays from here

Stockfish 17.1 at depth 20 rates the position −0.34: a slight edge for Black. Its three top choices for White:

  1. −0.34 7.O-O b5 8.Bd3 Bb7 9.Bf4 Be7
  2. −0.36 7.Bf4 Nge7 8.h4 b5 9.Be2 Bb7
  3. −0.45 7.Qe2 b5 8.Bd3 Bb7 9.O-O Bd6

Pawns, from White's side.

How it scores on lichess

805 rated lichess games reached this position; White scored 51.9%.

1200–159942.6%
1600–199954.3%
2000 and up51.2%

Light: White wins. Grey: draws. Dark: Black wins. About the sample.

Where it goes next

  • Smith-Morra Gambit Accepted, Morphy Defense Deferred7.O-O · rare

How to play against it

As White, castle quickly and keep the bishop on d3 after ...b5. Develop the dark-squared bishop to f4 before Black's knight reaches g6. Avoid a slow h3 or a3, since each tempo helps Black consolidate the extra pawn. Keep the rooks on the open c- and d-files.

Questions

What are the moves of the Sicilian Defense: Smith-Morra Gambit Accepted, Paulsen Formation?

The Sicilian Defense: Smith-Morra Gambit Accepted, Paulsen Formation starts 1.e4 c5 2.d4 cxd4 3.c3 dxc3 4.Nxc3 Nc6 5.Nf3 e6 6.Bc4 a6. Its ECO code is B21.

Is the Sicilian Defense: Smith-Morra Gambit Accepted, Paulsen Formation good for Black?

Stockfish 17.1 rates the position −0.34 at depth 20, which is a slight edge for Black. In 805 lichess games from our sample, White scored 51.9%. A solid choice for Black players who like queenside expansion, while White needs quick development to stay in the game.

What is the main idea of the Sicilian Defense: Smith-Morra Gambit Accepted, Paulsen Formation?

Black plays ...a6 to prepare ...b5 and ...Bb7, gaining time on White's bishop. White castles, puts the bishop on d3 and uses Bf4 and Rc1 to make the extra pawn hard to keep.

What should White play next?

The engine's first choice is O-O, with Bf4 and Qe2 close behind. 7.O-O completes White's kingside development first, so ...b5 and Bd3 come with White's king safe.

Updated October 2026. Sources and method.