Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. Nc3/3...Bb4/4. e5/4...c5/5. a3

=French Defence, Winawer Variation=

This is the main line of the Winawer Variation. Black's bishop is pinning white's c knight, and his c5 advance has just put additional pressure on white's center. At this point, white has chosen to regain the initiative by kicking out the bishop with 5.a3.

Black usually takes the knight with 5...Bxc3+, because moving 5...Ba5 leaves the c5 pawn undefended and open to white's 6.dxc5.

Theory table
1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 c5 5.a3